全文获取类型
收费全文 | 98536篇 |
免费 | 596篇 |
国内免费 | 885篇 |
专业分类
100017篇 |
出版年
2022年 | 32篇 |
2021年 | 69篇 |
2020年 | 33篇 |
2019年 | 50篇 |
2018年 | 11882篇 |
2017年 | 10713篇 |
2016年 | 7524篇 |
2015年 | 767篇 |
2014年 | 497篇 |
2013年 | 617篇 |
2012年 | 4542篇 |
2011年 | 13124篇 |
2010年 | 12202篇 |
2009年 | 8426篇 |
2008年 | 10065篇 |
2007年 | 11662篇 |
2006年 | 566篇 |
2005年 | 861篇 |
2004年 | 1263篇 |
2003年 | 1299篇 |
2002年 | 1036篇 |
2001年 | 368篇 |
2000年 | 285篇 |
1999年 | 135篇 |
1998年 | 87篇 |
1997年 | 76篇 |
1996年 | 66篇 |
1995年 | 59篇 |
1994年 | 68篇 |
1993年 | 67篇 |
1992年 | 107篇 |
1991年 | 120篇 |
1990年 | 71篇 |
1989年 | 68篇 |
1988年 | 79篇 |
1987年 | 65篇 |
1986年 | 41篇 |
1985年 | 47篇 |
1984年 | 45篇 |
1983年 | 58篇 |
1982年 | 29篇 |
1981年 | 40篇 |
1980年 | 24篇 |
1979年 | 25篇 |
1976年 | 21篇 |
1975年 | 22篇 |
1972年 | 250篇 |
1971年 | 280篇 |
1965年 | 19篇 |
1962年 | 26篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
Synthesis of Cell Coat in Normal and Transformed Cells 总被引:6,自引:0,他引:6
THE surface of transformed cells has been a focus of considerable attention recently because some of the properties which distinguish these cells from their precursors, such as decreased cell adhesiveness, altered cell orientation and loss of contact and density dependent inhibition1–3, may relate to changes on their surface. A common feature of vertebrate cells is the cell coat, a glycoprotein structure surrounding the plasma membrane4. Electron microscopy has revealed that transformed cells have a thicker coat than normal cells5 and we have now found that coat synthesis in cells transformed by an oncogenic DNA virus and in cells transformed by a chemical carcinogen occurs faster than in normal controls whereas only in the virus-transformed cells is the coat significantly thicker. 相似文献
992.
Alien chromosome addition lines have been widely used for identifying gene linkage groups, assigning species-specific characters
to a particular chromosome and comparing gene synteny between related species. In plant breeding, their utilization lies in
introgressing characters of agronomic value. The present investigation reports the production of intergeneric somatic hybrids
Brassica
napus (2n = 38) + Orychophragmus violaceus (2n = 24) through asymmetric fusions of mesophyll protoplasts and subsequent development of B. napus-O. violaceous chromosome addition lines. Somatic hybrids showed variations in morphology and fertility and were mixoploids (2n = 51–67) with a range of 19–28 O. violaceus chromosomes identified by genomic in situ hybridization (GISH). After pollinated with B. napus parent and following embryo rescue, 20 BC1 plants were obtained from one hybrid. These exhibited typical serrated leaves of O. violaceus or B. napus-type leaves. All BC1 plants were partially male fertile but female sterile because of abnormal ovules. These were mixoploids (2n = 41–54) with 9–16 chromosomes from O. violaceus. BC2 plants showed segregations for female fertility, leaf shape and still some chromosome variation (2n = 39–43) with 2–5 O. violaceus chromosomes, but mainly containing the whole complement from B. napus. Among the selfed progenies of BC2 plants, monosomic addition lines (2n = 39, AACC + 1O) with or without the serrated leaves of O. violaceus or female sterility were established. The complete set of additions is expected from this investigation. In addition, O. violaceus plants at diploid and tetraploid levels with some variations in morphology and chromosome numbers were regenerated from the
pretreated protoplasts by iodoacetate and UV-irradiation.
Z. Zhao and T. Hu make equal contributions to this work. 相似文献
993.
Wen Wang Yan Zhao Shujuan Yao Xiujuan Cui Wenying Pan Wenqian Huang Jiangang Gao Taotao Dong Shiqian Zhang 《Biochemistry. Biokhimii?a》2017,82(8):933-941
Epithelial ovarian cancer (EOC) has the highest mortality among various types of gynecological malignancies. Most patients die of metastasis and recurrence due to cisplatin resistance. Thus, it is urgent to develop novel therapies to cure this disease. CCK-8 assay showed that nigericin exhibited strong cytotoxicity on A2780 and SKOV3 cell lines. Flow cytometry indicated that nigericin could induce cell cycle arrest at G0/G1 phase and promote cell apoptosis. Boyden chamber assay revealed that nigericin could inhibit migration and invasion in a dose-dependent manner by suppressing epithelial–mesenchymal transition (EMT) in EOC cells. These effects were mediated, at least partly, by the Wnt/β-catenin signaling pathway. Our results demonstrated that nigericin could inhibit EMT during cell invasion and metastasis through the canonical Wnt/β-catenin signaling pathway. Nigericin may prove to be a novel therapeutic strategy that is effective in patients with metastatic EOC. 相似文献
994.
Telomerase expression strongly correlates with the grade of malignancy in glioma with inhibition illustrating a definite increase
in chemosensitivity. This study was designed to investigate the effects of a green tea derivative, epigallocatechin-3-gallate
(EGCG); together with either cisplatin or tamoxifen in glioma, and to investigate whether these effects are mediated through
telomerase suppression. EGCG showed a significant cytotoxic effect on 1321N1 cells after 24 h and on U87-MG cells after 72 h
(P < 0.001) without significantly affecting the normal astrocytes. Treatment with EGCG inhibited telomerase expression significantly
(P < 0.01) and enhanced the effect of cisplatin and tamoxifen in both 1321N1 (P < 0.01) and U87-MG (P < 0.001) cells. EGCG, as a natural product has enormous potential to be an anti-cancer agent capable of enhancing tumour
cell sensitivity to therapy. 相似文献
995.
In studying plant colonization by inoculated Fusarium oxysporum endophytes, it is important to be able to distinguish inoculated isolates from saprophytic strains. In the current study, F. oxysporum isolates were transformed with the green (GFP) and red fluorescent protein (DsRed) genes, and benomyl- and chlorate-resistant mutant isolates were also developed. The benomyl- and chlorate-resistant mutants, and the fluorescently labelled transformants, were able to grow on potato dextrose agar amended with 20 mg Benlate® l?1, 30 g chlorate l?1 and 150 μg hygromycin ml?1, respectively. Single spores of all mutants remained stable after several transfers on non-selective media. Most mutants and transformants produced colony diameters that did not differ significantly from that of their wild-type progenitors after 7 days of growth on non-selective media. Few mutants, however, had growth rates that were either slower or faster than for their wild-types. Plant colonization studies showed that root and rhizome tissue colonization by most benomyl- and chlorate-resistant mutants was similar to that of their wild-type isolates. Unlike GFP transformants, DsRed transformants were difficult to visualize in planta. Both the mutants and transformants can be used for future studies to investigate colonization, distribution and survival of biocontrol F. oxysporum endophytes in banana plants. 相似文献
996.
The effects of free mercury(II), cadmium(II) and lead(II) ions and their metalloporphyrin-derivatives on Trypanosoma brucei brucei growth in culture were studied. All experiments were conducted in the dark. IC(50) values on growth obtained in 24-h time-course experiments were 1.5 x 10(-7), 2.4 x 10(-6), 4.4 x 10(-6) and 2.6 x 10(-5) M for mercury(II) porphyrin, cadmium(II) porphyrin, lead(II) porphyrin and free base porphyrin, respectively. While the IC50 values for Hg2+, Cd2+ and Pb2+ were 3.6 x 10(-6), 1.5 x 10(-5) and 1.6 x 10(-5) M, respectively. These results clearly indicate that the toxicity of the metalloporphyrin complexes of mercury(II), cadmium(II) and lead(II) to T. b. brucei parasites was much higher compared to their free metal ions and free base porphyrin at low concentrations. It was also observed after 8 h incubation that the metalloporphyrins were effective in inhibiting the division of the parasites at concentrations >1.25 x 10(-7) M for mercury(II) porphyrin, concentrations >1.2 x 10(-6) M for cadmium(II) and lead(II) porphyrins and at concentrations >3.6 x 10(-6) M for Hg2+ ion. These observations were not detected in samples treated with the free metal ions and the free base porphyrin at the same concentrations. Interestingly, trypanosomes treated with metalloporphyrin complexes displayed different morphological features from those cells treated with free base porphyrin or metal ions. The chemotherapeutic potential of the metalloporphyrins of H2TMPyP for treatment of African trypanosomiasis is discussed. 相似文献
997.
The biomass and productivity of Schima superba-Castanopsis carlesii forests in Tiantong, Zhejiang Province, were determined using overlapping quadrants and stem analyses. The total community
biomass was (225.3±30.1) t hm−2, of which the aboveground parts accounted for 72.0% and the underground parts accounted for 28.0%. About 87.2% of biomass
existed in the tree layer. The resprouting biomass was small, of which over 95.0% occurred in the shrub layer. The productivity
of the aboveground parts of the community was (386.8±98.9) g m−2a−1, in which more than 96.0% was present at the tree level. The trunk’s contribution to productivity was the greatest, while
that of leaves was the smallest. In China, the community biomass of subtropical evergreen broadleaved forests differs significantly
with the age of the forest. The community biomass of the 52-year-old S. superba-C. carlesii forests in this study was lower than the average biomass of subtropical evergreen broadleaved forests in China, and was lower
than the biomass of other subtropical evergreen broadleaved forests elsewhere in the world. Moreover, its productivity was
lower than the model estimate, indicating that without disturbance, this community has great developmental potential in terms
of community biomass and productivity. 相似文献
998.
Nakazawa Y Sagane Y Kikuchi T Uchino M Nagai T Sato H Toeda K Takano K 《The protein journal》2010,29(8):598-608
We previously isolated Streptomyces racemochromogenes strain 10-3, which produces a phospholipase D (PLD) with high transphosphatidylation activity. Here, we purified and cloned
the PLD (PLD103) from the strain. PLD103 exerted the highest hydrolytic activity at a slightly alkaline pH, which is in contrast
to the majority of known Streptomyces PLDs that have a slightly acidic optimum pH. PLD103 shares only 71–76% amino acid sequence identity with other Streptomyces PLDs that have a slightly acidic optimum pH; thus, the diversity in the primary structure might explain the discrepancy observed
in the optimum pH. The purified PLD displayed high transphosphatidylation activity in the presence of glycerol, l-serine, and 2-aminoethanol hydrochloride with a conversion rate of 82–97% in a simple one-phase system, which was comparable
to the rate of other Streptomyces PLDs in a complicated biphasic system. 相似文献
999.
Daniela Giordano Roberta Russo Daniela Coppola Giovanna Altomonte Guido di Prisco Stefano Bruno Cinzia Verde 《Hydrobiologia》2015,761(1):293-312
Notothenioidei, the taxonomic group of teleosts that dominates the Southern Ocean and dwell in the Ross Sea at large, provide an example of marine species that underwent unique adaptations to life at low temperatures and high oxygen concentrations, resulting in morphological, physiological, genomic, and biochemical peculiarities in comparison with warm-water fish. Global Warming raises concerns over the fate of these stenothermal fish, as their adaptation has been accompanied by irreversible genomic losses, which suggest a poor genetic potential to adapt to warmer climates. Specifically, this review focuses on adaptation of proteins belonging to the globin superfamily, which include the respiratory proteins hemoglobin and myoglobin and the non-respiratory proteins neuroglobin and cytoglobin. Here, we describe their molecular adaptations to cold temperatures in the framework of the physiology of oxygen transport and management of oxidative stress in fish species largely populating the Ross Sea. 相似文献
1000.
The objectives of this work were to isolate the microorganisms responsible for a previously observed degradation of polycyclic
aromatic hydrocarbons (PAH) in soil and to test a method for cleaning a PAH-contaminated soil. An efficient PAH degrader was
isolated from an agricultural soil and designated as Mycobacterium LP1. In liquid culture, it degraded phenanthrene (58%), pyrene (24%), anthracene (21%) and benzo(a)pyrene (10%) present in mixture (initial concentration 50 μg ml−1 each) and phenanthrene (92%) and pyrene (94%) as sole carbon sources after 14 days of incubation at 30°C. In soil, Mycobacterium LP1 mineralised 14C-phenanthrene (45%) and 14C-pyrene (65%) after 10 days. The good ability of this Mycobacterium was combined with the benzo(a)pyrene oxidation effect obtained by 1% w/w rapeseed oil in a sequential treatment of a PAH-spiked soil (total PAH concentration
200 mg kg−1). The first step was incubation with the bacterium for 12 days and the second step was the addition of the rapeseed oil after
this time and a further incubation of 22 days. Phenanthrene (99%), pyrene (95%) and anthracene (99%) were mainly degraded
in the first 12 days and a total of 85% of benzo(a)pyrene was transformed during the whole process. The feasibility of the method is discussed. 相似文献