全文获取类型
收费全文 | 14029篇 |
免费 | 1203篇 |
国内免费 | 1篇 |
专业分类
15233篇 |
出版年
2024年 | 22篇 |
2023年 | 150篇 |
2022年 | 98篇 |
2021年 | 222篇 |
2020年 | 209篇 |
2019年 | 219篇 |
2018年 | 572篇 |
2017年 | 467篇 |
2016年 | 506篇 |
2015年 | 412篇 |
2014年 | 441篇 |
2013年 | 797篇 |
2012年 | 1136篇 |
2011年 | 1295篇 |
2010年 | 673篇 |
2009年 | 439篇 |
2008年 | 958篇 |
2007年 | 866篇 |
2006年 | 851篇 |
2005年 | 642篇 |
2004年 | 672篇 |
2003年 | 622篇 |
2002年 | 560篇 |
2001年 | 412篇 |
2000年 | 524篇 |
1999年 | 261篇 |
1998年 | 140篇 |
1997年 | 98篇 |
1996年 | 94篇 |
1995年 | 78篇 |
1994年 | 78篇 |
1993年 | 75篇 |
1992年 | 71篇 |
1991年 | 68篇 |
1990年 | 41篇 |
1989年 | 29篇 |
1988年 | 33篇 |
1987年 | 33篇 |
1986年 | 16篇 |
1985年 | 42篇 |
1984年 | 27篇 |
1983年 | 26篇 |
1982年 | 32篇 |
1981年 | 23篇 |
1980年 | 22篇 |
1979年 | 25篇 |
1978年 | 22篇 |
1977年 | 19篇 |
1974年 | 18篇 |
1973年 | 17篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
101.
Nuñez GG Malmassari SL Costantino SN Venturiello SM 《The Journal of parasitology》2000,86(5):1121-1124
An immunoelectrotransfer blot assay (IETB) using excretory secretory products of muscle larvae of Trichinella spiralis (ML-ESP) and the avidin biotin system was developed in order to characterize reactivity against ML-ESP in sera from patients with acute and chronic trichinellosis. A complete pattern of up to 13 bands was developed by sera from individuals with trichinellosis where doublets, triplets, or single bands were shown to have molecular weights of roughly 66, 55, 45, 36, 29, 24, and 14 kDa. The bands at approximately 55, 36, 29, and 14 kDa proved specific for T. spiralis. The band at approximately 55 kDa was present in all trichinellosis sera, whereas the approximately 14-kDa band was present in only a small percentage of sera. The development of approximately 36- and 29-kDa bands suggests a modulation of the reactivity against ML-ESP over time. IETB proved more sensitive for the population of chronic trichinellosis under study than a conventional diagnostic enzyme-linked immunosorbent assay, allowing negative or borderline serum samples to be determined. Thus, this technique, when applied for human trichinellosis surveillance, should provide a useful tool in endemic areas. 相似文献
102.
González-Mariscal L Islas S Contreras RG García-Villegas MR Betanzos A Vega J Diaz-Quiñónez A Martín-Orozco N Ortiz-Navarrete V Cereijido M Valdés J 《Experimental cell research》1999,248(1):97-109
Most of the information on the structure and function of the tight junction (TJ) has been obtained in MDCK cells. Accordingly, we have sequenced ZO-1 in this cell type, because this protein is involved in the response of the TJ to changes in Ca2+, phosphorylation, and the cytoskeleton. ZO-1 of MDCK cells comprises 6805 bp with a predicted open reading frame of 1769 amino acids. This sequence is 92 and 87% homologous to human and mouse ZO-1, respectively. Two nuclear sorting signals located at the PDZ1 and GK domains and 17 SH3 putative binding sites at the proline-rich domain were detected. We found two new splicing regions at the proline-rich region: beta had not been reported in human and mouse counterparts, and gamma, which was previously sequenced in human and mouse ZO-1, is now identified as a splicing region. The expression of different beta and gamma isoforms varies according to the tissue tested. With the information provided by the sequence, Southern blot, and PCR experiments we can predict a single genomic copy of MDCK-ZO-1 that is at least 13.16 kb long. MDCK-ZO-1 mRNA is 7.4 kb long. Its expression is regulated by calcium, while the expression of MDCK-ZO-1 protein is not. 相似文献
103.
Goñi F López R Etxeandia A Millán E Amiano P 《Journal of chromatography. B, Analytical technologies in the biomedical and life sciences》2007,852(1-2):15-21
An improved method for the determination of selected organochlorine pesticides (OCPs) and polychlorinated biphenyls (PCBs) in human serum was developed. The method requires low volume of serum (500 microl) and 48-96 samples per day can be prepared by one analyst without special automatic equipment. Initial extraction was performed using 96-well solid-phase extraction disk plates and was followed by a clean-up with silica gel/sulfuric acid. Different denaturation, elution and clean-up conditions were tested. Quantification was carried out by gas chromatography equipped with electron capture detector (GC-ECD) or mass spectrometer (GC-MS). Recoveries of PCB congeners 28, 52, 101, 118, 138, 153 and 180 and OCPs HCB, beta-HCH, p,p'-DDE and p,p'-DDT at two spiking levels (n=8) varied from 57 to 120%, and intra-day relative standard deviation from 1 to 11%, both depending on spiking level and compound. Inter-day relative standard deviation was <15% in all cases. Limit of quantification (LOQ) for these PCBs ranged from 0.08 to 0.13 ng/ml and for these OCPs from 0.16 to 0.40 ng/ml. The optimized method was applied to the analysis of 1000 serum samples from different places of Spain. 相似文献
104.
Franco Chimenti Daniela Secci Adriana Bolasco Paola Chimenti Arianna Granese Simone Carradori Elias Maccioni M. Cristina Cardia Matilde Yáñez Francisco Orallo Stefano Alcaro Francesco Ortuso Roberto Cirilli Rosella Ferretti Simona Distinto Johannes Kirchmair Thierry Langer 《Bioorganic & medicinal chemistry》2010,18(14):5063-5070
The present study reports on synthesis in high yields (70–99%), HPLC enantioseparation, inhibitory activity against human monoamino oxidases, and molecular modeling including 3D-QSAR studies, of a large series of (4-aryl-thiazol-2-yl)hydrazones (1–45). Most of the synthesized compounds proved to be potent and selective inhibitors of hMAO-B isoform in the micromolar or nanomolar range, thus demonstrating that hydrazothiazole could be considered a good pharmacophore to design new hMAO-B inhibitors. Due to the presence in some derivatives of a chiral center, we also performed a semipreparative chromatographic enantioseparation of these compounds obtained by a stereoconservative pattern. The separated enantiomers were submitted to in vitro biological evaluation to point out the stereorecognition of the active site of the enzyme towards these structures. Finally, a 3D-QSAR study was carried out using Comparative Molecular Field Analysis (CoMFA), aiming to deduce rational guidelines for the further structural modification of these lead compounds. 相似文献
105.
In this paper some examples of the development of communities of microorganisms and plants on historic buildings and montiments
are shown. When the building stones differ from the surrounding natural substrata, an increase in the biological diversity
of the area is produced. In some cases, monuments can come to constitute a true refuge for a few species when the natural
habitat is threatened. It is suggested that biological diversity, when it does not represent a threat for the cultural heritage,
should be considered worthy of preservation. 相似文献
106.
Sergio Padilla-López María Jiménez-Hidalgo Alejandro Martín-Montalvo Catherine F. Clarke Plácido Navas Carlos Santos-Ocaña 《生物化学与生物物理学报:生物膜》2009,1788(6):1238-1248
Coenzyme Q is an isoprenylated benzoquinone lipid that functions in respiratory electron transport and as a lipid antioxidant. Dietary supplementation with Q is increasingly used as a therapeutic for treatment of mitochondrial and neurodegenerative diseases, yet little is known regarding the mechanism of its uptake. As opposed to other yeast backgrounds, EG103 strains are unable to import exogenous Q6 to the mitochondria. Furthermore, the distribution of exogenous Q6 among endomembranes suggests an impairment of the membrane traffic at the level of the endocytic pathway. This fact was confirmed after the detection of defects in the incorporation of FM4-64 marker and CPY delivery to the vacuole. A similar effect was demonstrated in double mutant strains in Q6 synthesis and several steps of endocytic process; those cells are unable to uptake exogenous Q6 to the mitochondria and restore the growth on non-fermentable carbon sources. Additional data about the positive effect of peptone presence for exogenous Q6 uptake support the hypothesis that Q6 is transported to mitochondria through an endocytic-based system. 相似文献
107.
P. Madejón L. Ciadamidaro T. Marañón J. M. Murillo 《International journal of phytoremediation》2013,15(6):602-614
Phytostabilization aims to immobilize soil contaminants using higher plants. The accumulation of trace elements in Populus alba leaves was monitored for 12 years after a mine spill. Concentrations of As and Pb significantly decreased, while concentrations of Cd and Zn did not significantly over time. Soil concentrations extracted by CaCl2 were measured by ICP-OES and results of As and Pb were below the detection limit. Long-term biomonitoring of soil contamination using poplar leaves was proven to be better suited for the study of trace elements. Plants suitable for phytostabilization must also be able to survive and reproduce in contaminated soils. Concentrations of trace elements were also measured in P. alba fruiting catkins to determine the effect on its reproduction potential. Cadmium and Zn were found to accumulate in fruiting catkins, with the transfer coefficient for Cd significantly greater than Zn. It is possible for trace elements to translocate to seed, which presents a concern for seed germination, establishment and colonization. We conclude that white poplar is a suitable tree for long-term monitoring of soil contaminated with Cd and Zn, and for phytostabilization in riparian habitats, although some caution should be taken with the possible effects on the food web.
Supplemental materials are available for this article. Go to the publisher's online edition of International Journal of Phytoremediation to view the supplemental file. 相似文献
108.
Molecular and morphological diversity of Trebouxia microalgae in sphaerothallioid Circinaria spp. lichens1 下载免费PDF全文
Arántzazu Molins Francisco J. García‐Breijo José Reig‐Armiñana Eva Barreno 《Journal of phycology》2018,54(4):494-504
Three vagrant (Circinaria hispida, Circinaria gyrosa, and Circinaria sp. ‘paramerae’) and one crustose (semi‐vagrant, Circinaria sp. ‘oromediterranea’) lichens growing in very continental areas in the Iberian Peninsula were selected to study the phycobiont diversity. Mycobiont identification was checked using nrITS DNA barcoding: Circinaria sp. ‘oromediterranea’ and Circinaria sp. ‘paramerae’ formed a new clade. Phycobiont diversity was analyzed in 50 thalli of Circinaria spp. using nrITS DNA and LSU rDNA, with microalgae coexistence being found in all the species analyzed by Sanger sequencing. The survey of phycobiont diversity showed up to four different Trebouxia spp. as the primary phycobiont in 20 thalli of C. hispida, in comparison with the remaining Circinaria spp., where only one Trebouxia was the primary microalga. In lichen species showing coexistence, some complementary approaches are needed (454 pyrosequencing and/or ultrastructural analyses). Five specimens were selected for high‐throughput screening (HTS) analyses: 22 Trebouxia OTUs were detected, 10 of them not previously known. TEM analyses showed three different cell morphotypes (Trebouxia sp. OTU A12, OTU S51, and T. cretacea) whose ultrastructure is described here in detail for the first time. HTS revealed a different microalgae pool in each species studied, and we cannot assume a specific pattern between these pools and the ecological and/or morphological characteristics. The mechanisms involved in the selection of the primary phycobiont and the other microalgae by the mycobiont are unknown, and require complex experimental designs. The systematics of the genus Circinaria is not yet well resolved, and more analyses are needed to establish a precise delimitation of the species. 相似文献
109.
Alcohol exposure alters the expression pattern of neural cell adhesion molecules during brain development 总被引:11,自引:0,他引:11
Miñana R Climent E Barettino D Segui JM Renau-Piqueras J Guerri C 《Journal of neurochemistry》2000,75(3):954-964
Neural cell adhesion molecules (NCAMs) play critical roles during development of the nervous system. The aim of this study is to investigate the possible effect of ethanol exposure on the pattern of expression and sialylation of NCAM isoforms during postnatal rat brain development because alterations in NCAM content and distribution have been associated with defects in cell migration, synapse formation, and memory consolidation, and deficits in these processes have been observed after in utero alcohol exposure. The expression of NCAM isoforms in the developing cerebral cortex of pups from control and alcohol-fed mothers was assessed by western blotting, ribonuclease protection assay, and immunocytochemistry. The highly sialylated form of NCAM [polysialic acid (PSA)-NCAM] is mainly expressed during the neonatal period and then is down-regulated in parallel with the appearance of NCAM 180 and NCAM 140. Ethanol exposure increases PSA-NCAM levels during the neonatal period, delays the loss of PSA-NCAM, decreases the amount of NCAM 180 and NCAM 140 isoforms, and reduces sialyltransferase activity during postnatal brain development. Neuraminidase treatment of ethanol-exposed neonatal brains leads to more intense band degradation products, suggesting a higher content of NCAM polypeptides carrying PSA in these samples. However, NCAM mRNA levels are not changed by ethanol. Immunocytochemical analysis demonstrates that ethanol triggers an increase in PSA-NCAM immunolabeling in the cytoplasm of astroglial cells, accompanied by a decrease in immunogold particles over the plasma membrane. These findings indicate that ethanol exposure during brain development alters the pattern of NCAM expression and suggest that modification of NCAM could affect neuronal-glial interactions that might contribute to the brain defects observed after in utero alcohol exposure. 相似文献
110.
Sudano MJ Paschoal DM Rascado Tda S Magalhães LC Crocomo LF de Lima-Neto JF Landim-Alvarenga Fda C 《Theriogenology》2011,75(7):1211-1220
The objective was to evaluate supplementation of fetal calf serum (FCS) and phenazine ethosulfate (PES), a metabolic regulator that inhibits fatty acid synthesis, in culture media during in vitro production (IVP) of bovine embryos. Taking oocyte fertilization (n = 4,320) as Day 0, four concentrations of FCS (0, 2.5, 5, and 10%) and three periods of exposure to PES (without addition—Control; after 60 h—PES Day 2.5 of embryo culture; and after 96 h—PES Day 4) were evaluated. Increasing FCS concentration in the culture media enhanced lipid accumulation (P < 0.05), increased apoptosis in fresh (2.5%: 19.1 ± 1.8 vs 10%: 28.4 ± 2.3, P < 0.05; mean ± SEM) and vitrified (2.5%: 42.8 ± 2.7 vs 10%: 69.2 ± 3.4, P < 0.05) blastocysts, and reduced blastocoele re-expansion after vitrification (2.5%: 81.6 ± 2.5 vs 10%: 67.3 ± 3.5, P < 0.05). The addition of PES in culture media, either from Days 2.5 or 4, reduced lipid accumulation (P < 0.05) and increased blastocoele re-expansion after vitrification (Control: 72.0 ± 3.0 vs PES Day 2.5: 79.9 ± 2.8 or PES Day 4: 86.2 ± 2.4, P < 0.05). However, just the use of PES from D4 reduced apoptosis in vitrified blastocysts (Control: 52.0 ± 3.0 vs PES Day 4: 39.2 ± 2.4, P < 0.05). Independent of FCS withdrawal or PES addition to culture media, the in vivo control group had lesser lipid accumulation, a lower apoptosis rate, and greater cryotolerance (P < 0.05). The increased lipid content was moderately correlated with apoptosis in vitrified blastocysts (r = 0.64, P = 0.01). In contrast, the increased apoptosis in fresh blastocysts was strongly correlated with apoptosis in vitrified blastocysts (r = 0.94, P < 0.0001). Therefore, using only 2.5% FCS and the addition of PES from Day 4, increased the survival of IVP embryos after vitrification. Moreover, embryo quality, represented by the fresh apoptosis rate, was better than lipid content for predicting embryo survival after vitrification. 相似文献