全文获取类型
收费全文 | 16528篇 |
免费 | 1063篇 |
国内免费 | 3篇 |
出版年
2024年 | 16篇 |
2023年 | 167篇 |
2022年 | 281篇 |
2021年 | 527篇 |
2020年 | 365篇 |
2019年 | 417篇 |
2018年 | 597篇 |
2017年 | 515篇 |
2016年 | 677篇 |
2015年 | 888篇 |
2014年 | 990篇 |
2013年 | 1198篇 |
2012年 | 1317篇 |
2011年 | 1294篇 |
2010年 | 819篇 |
2009年 | 692篇 |
2008年 | 882篇 |
2007年 | 856篇 |
2006年 | 790篇 |
2005年 | 607篇 |
2004年 | 566篇 |
2003年 | 466篇 |
2002年 | 423篇 |
2001年 | 286篇 |
2000年 | 272篇 |
1999年 | 209篇 |
1998年 | 117篇 |
1997年 | 75篇 |
1996年 | 72篇 |
1995年 | 72篇 |
1994年 | 66篇 |
1993年 | 54篇 |
1992年 | 101篇 |
1991年 | 96篇 |
1990年 | 83篇 |
1989年 | 64篇 |
1988年 | 64篇 |
1987年 | 56篇 |
1986年 | 54篇 |
1985年 | 45篇 |
1984年 | 47篇 |
1983年 | 33篇 |
1982年 | 32篇 |
1981年 | 32篇 |
1980年 | 26篇 |
1979年 | 36篇 |
1978年 | 34篇 |
1976年 | 20篇 |
1975年 | 31篇 |
1974年 | 17篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
871.
Murine models offer potential insights regarding human cardiac disease, but efficient and reliable methods for phenotype evaluation are necessary. We employed non-invasive electrocardiography (ECG) in mice, investigating statistical reliability of these parameters with respect to anesthetic and animal age. Mice (C57BL/6, 8 or 48 weeks) were anesthetized by ketamine/xylazine (K/X, 80/10 mg/kg ip) or by inhalation anesthetic (halothane, HAL; sevoflurane, SEV) and 6 lead ECGs were recorded. P wave duration and QT interval was significantly prolonged with K/X compared to HAL and SEV, indicating slowed atrial and ventricular conduction. P-R interval (atrio-ventricular conduction) was significantly increased in aged mice under all anesthetics. Heart rate was inversely correlated to QT interval and P wave duration. We also detected significant age effects with respect to optimal approaches for QT interval corrections. Power analysis showed 4-fold higher number of mice/group, were required for K/X, to achieve identical statistical sensitivity. These data demonstrate the importance of anesthetic selection for relevant and reliable ECG analysis in mice and illustrate the selective influences of anesthetics and age on cardiac conductance in this species. 相似文献
872.
The sesquiterpene lactone tubiferin was chemically purified from the brazilian native plant Wunderlichia crulsiana and identified by NMR and GC/MS data. Its ability to inhibit the respiratory burst of peritoneal inflammatory polymorphonuclear leukocytes (PMN) stimulated upon addition of phorbol miristate acetate (PMA), opsonized zymosan (OZ), and N-formyl-methionyl-leucyl-phenylalanine (fMLP) was evaluated. The tubiferin inhibition was more pronounced when PMN were stimulated through the protein kinase C pathway (PMA) compared to the alternative complement pathway (OZ). The inhibition when PMN were triggered by a chemoattractant stimulus (fMLP) was similar to that achieved with OZ-stimulated phagocytes. Tubiferin showed dose-dependent effects on the PMN respiratory burst triggered by the three different substances, and also decreased substantially the carrageenan-induced mice paw edema. 相似文献
873.
Jabłońska E Puzewska W Marcińczyk M Hermanowska-Szpakowicz T 《Medycyna do?wiadczalna i mikrobiologia》2003,55(1):81-87
The aim of this study was to estimate the release of IL-6 by human neutrophils (PMN) and peripheral blood mononuclear cells (PBMC) in patients with Lyme disease confronted with the serum levels. The cells were isolated from whole blood of 25 patients and of 10 healthy donors and cultured in the presence of LPS. In the culture supernatants and serum the concentration of IL-6 with ELISA (BioSource) were measured. In patients we observed higher values of IL-6 released by unstimulated PMN and PBMC in compared with control. In contrast to control, we didn't observe increased the release of IL-6 by LPS-stimulated PMN and PBMC as compared to unstimulated cells. In the serum of patient we found increased the concentration of IL-6. The higher ability of PMN and PBMC from patients with Lyme disease to release of IL-6 and the lack response to additional stimulation indicate the activation of PMN and PBMC in vivo. 相似文献
874.
Mutagenic activity as a parameter to assess ambient air quality for protection of the environment and human health 总被引:6,自引:0,他引:6
Vargas VM 《Mutation research》2003,544(2-3):313-319
Atmospheric pollution has significant effects on maintaining the integrity of ecosystems and on the population's quality of life. Epidemiological studies have clearly associated related health problems, especially respiratory diseases, with exposure to air pollution. Organic compounds adsorbed to the airborne particulate matter are mutagenic in the Salmonella/microsome assay, and a considerable number of them are known to be carcinogenic to rodents. Studies performed at four sites within the urban area of Porto Alegre, capital of the state of Rio Grande do Sul, identified higher mutagenic activity at the sites with heavier vehicle traffic in assays without and with metabolic activation. The responses varied at different seasons of the year, and the highest revertants per cubic meter (rev/m(3)) values were observed in spring for moderately polar compounds, and in summer for non-polar ones. A pilot study was also performed in the region under the influence of a industrial petrochemical area. Most of the sites studied within the industrial area, as compared to others sampled in the nearby environment, presented higher levels of mutagenic activity independent of total suspended particulates (TSP) concentration in the sample. In the urban and industrial regions, the observed mutagenic activities were strongly associated with the presence of polycyclic aromatic hydrocarbons (PAHs). The responses observed in the TA98NR and TA98/1,8-DNP(6) strains suggest the activity of nitrocompounds in both studies. The Salmonella/microsome assay is a sensitive method to define areas contaminated by these compounds, even in samples with TSP values that are consistent with the legal environmental quality standards. 相似文献
875.
Agaricus blazei Murill is a medicinal mushroom native to Brazil. The present work assessed the clastogenic and anticlastogenic potential of organic extracts (ethanol and chloroform/methanol) from the lineage AB97/11 in chinese hamster CHO-K(1) (wild type) and CHO-xrs5 (repair deficient) cells using the chromosome aberration (CA) and sister chromatid exchange (SCE) assays. In these experimental conditions were observed: (a) anticlastogenic effect at concentrations of 0.06 and 0.09% of the EtOH extract and at the 0.03 and 0.06% concentrations of the C/MetOH extract in CHO-K(1); (b) absence of protector effect on CHO-xrs5 cells; and (c) absence of protector effect in the SCE assay. These results indicate that organic extracts of A. blazei lineage AB97/11 present bio-antimutagenic type protective activity. 相似文献
876.
Domínguez MG Wong-Ley LE Rivera H Vásquez AI Ramos AL Sánchez-Urbina R Morales JA Figuera LE 《Annales de génétique》2003,46(1):45-48
There have only been eight patients with 6p pure trisomy involving different segments: four cases resulted from a translocation or insertion and four were due to an intrachromosomal duplication. We report here the first postnatally ascertained patient with a pure 6p partial trisomy due to an interchromosomal insertion (16;6)(p12;p21.2p23)mat. This rearrangement was confirmed by fluorescent in situ hybridization (FISH) with whole chromosome 6 and 16 painting probes. The clinical findings in the present patient were similar to those observed in previous cases, including craniofacial dysmorphism, minor anomalies, and lack of severe anatomical defects; yet, the unspecificity of many of these features prevented us from delineating the 6p pure trisomy syndrome. 相似文献
877.
878.
Chara tomentosa antheridial plasmodesmata are described during proliferation and spermiogenesis. In antheridial filament cells which are
cycling completely synchronously, unplugged plasmodesmata are filled with light cytoplasm. The same plasmodesmata are observed
after cessation of mitotic division followed by the onset of synchronous spermiogenesis. Walls separating cells at different
cell cycle stages and dividing antheridial filaments into asynchronous domains are plugged with a dense osmophilic substance.
Similarly plugged plasmodesmata are present between antheridial cells of different types, e.g., capitular cells and antheridial filaments. In mid spermiogenesis when abundant endoplasmic reticulum (ER) appears temporarily
it penetrates into plasmodesmata enabling cell-to-cell transport via ER cisternae. In late spermiogenesis there are no cisternae
in plasmodesmata.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
879.
Filgueira de Azevedo W dos Santos GC dos Santos DM Olivieri JR Canduri F Silva RG Basso LA Renard G da Fonseca IO Mendes MA Palma MS Santos DS 《Biochemical and biophysical research communications》2003,309(4):923-928
Docking simulations have been used to assess protein complexes with some success. Small angle X-ray scattering (SAXS) is a well-established technique to investigate protein spatial configuration. This work describes the integration of geometric docking with SAXS to investigate the quaternary structure of recombinant human purine nucleoside phosphorylase (PNP). This enzyme catalyzes the reversible phosphorolysis of N-ribosidic bonds of purine nucleosides and deoxynucleosides. A genetic deficiency due to mutations in the gene encoding for PNP causes gradual decrease in T-cell immunity. Inappropriate activation of T-cells has been implicated in several clinically relevant human conditions such as transplant rejection, rheumatoid arthritis, lupus, and T-cell lymphomas. PNP is therefore a target for inhibitor development aiming at T-cell immune response modulation and has been submitted to extensive structure-based drug design. The present analysis confirms the trimeric structure observed in the crystal. The potential application of the present procedure to other systems is discussed. 相似文献
880.
Zień P Bretner M Zastapiło K Szyszka R Shugar D 《Biochemical and biophysical research communications》2003,306(1):129-133
Like the previously reported 4,5,6,7-tetrabromobenzotriazole (TBBt), the structurally related 4,5,6,7-tetrabromobenzimidazole (TBBz) is a selective ATP-competitive inhibitor of protein kinase CK2 from such divergent sources as yeast, rat liver, Neurospora crassa and Candida tropicalis, with K(i) values in the range 0.5-1 microM. It is virtually inactive vs. PKA, PKC, and a very weak inhibitor of protein kinase CK1. The corresponding tetrachlorobenzimidazole (TCBz) is a much weaker inhibitor of CK2, like tetrachlorobenzotriazole (TCBt) relative to TBBt. Bearing in mind the similarity of the van der Waals radii of Br (1.95 A) and CH(3) (2.0 A), the corresponding much less hydrophobic 4,5,6,7-tetramethylbenzotriazole (TMeBt) was prepared and found to be a very weak inhibitor of CK2, as well as of CK1. An unexpected, and significant, difference between TBBt and TBBz are their inhibitory activities vs. the yeast protein kinase PK60S, which phosphorylates, both in vitro and in intact yeast cells, three of the five pp13 kDa ribosomal surface acidic proteins in yeast cells. TBBt was previously noted to be a more effective inhibitor of PK60S than of yeast CK2; by contrast, TBBz is a relatively feeble inhibitor of PK60S, hence more selective than TBBt vs. CK2 in yeast cells. TMeBt was virtually inactive vs PK60S. Like TBBt, TBBz is an additional lead compound for development of more potent inhibitors of CK2. 相似文献