全文获取类型
收费全文 | 4493篇 |
免费 | 335篇 |
国内免费 | 2篇 |
专业分类
4830篇 |
出版年
2023年 | 18篇 |
2022年 | 39篇 |
2021年 | 78篇 |
2020年 | 38篇 |
2019年 | 53篇 |
2018年 | 108篇 |
2017年 | 107篇 |
2016年 | 161篇 |
2015年 | 218篇 |
2014年 | 226篇 |
2013年 | 278篇 |
2012年 | 327篇 |
2011年 | 331篇 |
2010年 | 225篇 |
2009年 | 196篇 |
2008年 | 231篇 |
2007年 | 254篇 |
2006年 | 207篇 |
2005年 | 202篇 |
2004年 | 182篇 |
2003年 | 137篇 |
2002年 | 143篇 |
2001年 | 115篇 |
2000年 | 66篇 |
1999年 | 60篇 |
1998年 | 45篇 |
1997年 | 25篇 |
1996年 | 30篇 |
1995年 | 32篇 |
1994年 | 27篇 |
1993年 | 25篇 |
1992年 | 42篇 |
1991年 | 26篇 |
1990年 | 38篇 |
1989年 | 36篇 |
1988年 | 27篇 |
1987年 | 38篇 |
1986年 | 20篇 |
1985年 | 22篇 |
1984年 | 24篇 |
1983年 | 22篇 |
1982年 | 19篇 |
1981年 | 19篇 |
1977年 | 21篇 |
1976年 | 22篇 |
1975年 | 27篇 |
1974年 | 19篇 |
1973年 | 20篇 |
1971年 | 17篇 |
1966年 | 17篇 |
排序方式: 共有4830条查询结果,搜索用时 0 毫秒
21.
A methodology is proposed for assessing the ecological value of streams in the catchment of the Moravská Dyje River. It is concluded that by using a wide range of parameters that a more objective assessment is achieved than if only one were used. The landscape of the catchment studied contains excessive amounts of nutrients and, in comparison to its natural state, has become too uniform. 相似文献
22.
Living yeast cells can be selectively stained with the lipophilic cationic cyanine dye DiOC6(3) in a mitochondrial membrane potential-dependent manner. Our study extends the use of flow cytometric analysis and sorting to DiOC6(3)-stained yeast cells. Experimental conditions were developed that prevented the toxic side effect of the probe and gave a quantitative correlation between fluorescence and mitochondrial membrane potential, without any staining of other membranes. The localization of the fluorochrome was checked by confocal microscopy and image cytometry. The mitochondrial membrane alterations were also tested through cardiolipin staining with nonyl acridine orange. Differences in light scattering and in fluorescence were detected in mutants (rho-, rho degrees, mit-, or pet-) and wild-type (rho+mit+) populations of yeast. The dye uptake of respiratory-deficient yeast strains was significantly reduced as compared to that of the wild-type. Application of an uncoupler (mCICCP), which collapsed the mitochondrial membrane potential (alphapsi(m)), led to a drastic reduction of the dye uptake. It was observed that a decrease in deltapsi(m), was usually correlated with a decrease in cardiolipin stainability by nonyl acridine orange (NAO). Quantitative flow cytometry is a fast and reproducible technique for rapid screening of yeast strains that might be suspected of respiratory dysfunction and/or mitochondrial structural changes. We give evidence that it is an adequate method to characterize and isolate respiratory mutants through sorting procedure, with selective enrichment of the population studied in respiring or non-respiring yeast cells. Confocal microscopy and image cytometry corroborate the flow cytometry results. 相似文献
23.
A new gene coding for an antigen recognized by autologous cytolytic T lymphocytes on a human renal carcinoma 总被引:7,自引:0,他引:7
Béatrice Gaugler Nathalie Brouwenstijn Valérie Vantomme Jean-Pierre Szikora Corry W. Van der Spek Jean-Jacques Patard Thierry Boon Peter Schrier Benoît J. Van den Eynde 《Immunogenetics》1996,44(5):323-330
Previous reports have described antigens that are recognized on human melanoma cells by autologous cytolytic T lymphocytes
(CTL). The genes coding for a number of these antigens have been identified. Here we report the cloning of a gene that codes
for an antigen recognized by autologous CTL on a human renal carcinoma cell line. This antigen is presented byHLA-B7 and is encoded by a new gene that we have namedRAGE1. No expression ofRAGE1 was found in normal tissues other than retina. RAGE1 expression was found in only one of 57 renal cell carcinoma samples,
and also in some sarcomas, infiltrating bladder carcinomas, and melanomas. This represents the first identification of an
antigen recognized by autologous CTL on a renal tumor. 相似文献
24.
Vascular endothelial cells: Targets for studying the activity of hair follicle cell-produced VEGF 总被引:1,自引:0,他引:1
S. Lachgar M. Charvéron Y. Gall J. Plouët J. L. Bonafé 《Cell biology and toxicology》1996,12(4-6):331-334
Fetal bovine aortic endothelial cells (FBAEC) were exposed to purified fractions of conditioned medium from cultures of hair dermal papilla cells (DPC) to determine the existence of any vascular endothelial growth factor (VEGF)-like paracrine activity of the latter. Such fractions were tested for stimulation of growth and migration of cultured FBAEC. In addition, VEGF secretion by DPC was measured by radioassay of VEGF receptors using FBAEC as target cells. The results showed that stimulation of FBAEC proliferation and migration following exposure to purified conditioned medium was dose-dependent. Radioreceptor assays of recombinant VEGF and purified DPC-conditioned medium showed competitive VEGF binding in FBAEC.Abbreviations CM
conditioned medium
- DMEM
Dulbecco's modified eagle's medium
- DPC
dermal papilla cells
- EDTA
ethylenediaminetetra-acetic acid
- FBAEC
fetal bovine aortic endothelial cells
- FCS
fetal calf serum
- VEGF
vascular endothelial growth factor 相似文献
25.
The techniques of 27Al- and 31P-nuclear magnetic resonance (NMR) spectroscopy were used to investigate the interactions of aluminium with intracellular ligands within the mycelium of the ectomycorrhizal basidiomycete Laccaria bicolor (Maire) Orton (S238). The vegetative mycelium was grown on medium containing 0.5 mM AlCl3 for 0.5 to 3 d. The 27Al-NMR spectra showed that aluminium was rapidly taken up and accumulated into polyphosphate complexes in the vacuole. Comparison with Al-polyphosphate complexes obtained in vitro on model systems indicated that Al forms at least three mixed-solvation complexes with Pi and polyphosphates, that there is more than one complex present under any set of conditions, and that the equilibrium between these complexes shifts dramatically with Al concentration in the medium. The high phosphate concentrations in the growth medium favoured the accumulation of the Al-polyphosphate complexes. When mycelium containing Al-polyphosphate complexes was transferred to Al-free nutrient solution for 9 d, the Alpolyphosphate complexes were not remobilized. The sequestration of Al in the polyphosphate complexes could therefore make a significant contribution to the protection of mycorrhizal plants against aluminium toxicity.Abbreviations NMR
nuclear magnetic resonance
- PolyP
polyphosphate(s)
- PP1
terminal phosphate of PolyP
- PP3
middle phosphate of PolyP
We thank Prof. Daniel Canet (Laboratoire de Méthodologie RMN, University of Nancy I, Vandceuvre-lès-Nancy, France) for his constant encouragement and Christine Delaruelle for skilled technical assistance in growing the fungal cultures. This work was supported by a research grant from the Commission of the European Communities (STEP-CT90-0059, Role of Ectomycorrhiza in Stress Tolerance of Forest Trees) to F.M. and a travel grant from the Institut National de la Recherche Agronomique to I.K.; R.C. is a recipient of a Postdoctoral Fellowship from the Natural Sciences and Engineering Research Council of Canada. 相似文献
26.
Biochemical profiles on API Rapid CH* strips and protein profiles on polyacrylamide gels in the presence of sodium dodecyl sulfate were used to distinguish two
strains of the entomopathogenic fungusBeauveria bassiana (Balsamo) Vuillemin, ARSEF 2991 and ATCC 44860. Next, the toxicity of these two strains was determined at concentrations
of 102, 104, 106 and 108 blastospores/ml on larvae of the Colorado potato beetleLeptinotarsa decemlineata Say (Coleoptera: Chrysomelidae) and of its predator, the spotted ladybird beetle,Coleomegilla maculata lengi Timberlake (Coleoptera: Coccinellidae).
Both strains were highly toxic toL. decemlineata larvae. However, the two strains exhibited different levels of toxicity forC. maculata larvae: ARSEF 2991 was toxic, whereas ATCC 44860 caused little coccinellid larval mortality.
Résumé Les profils biochimiques sur galeries API Rapid CH* et les profils protéiques sur gels de polyacrylamide ont été utilisés pour distinguer deux souches du champignon entomopathogèneBeauveria bassiana (Balsamo) Vuillemin. La toxicité de ces deux souches a été déterminée à des concentrations de 102, 104, 106 et 108 blastospores/ml sur des larves du doryphore,Leptinotarsa decemlineata Say (Coleoptera: Chrysomelidae) et de la coccinelle maculéeColeomegilla maculata lengi Timberlake (Coleoptera: Coccinellidae). Les deux souches deB. bassiana se sont avérées actives à l'égard des larves deL. decemlineata. Toutefois la souche ARSEF 2991 s'est avérée pathogène pour les larves deC. maculata, alors que la souche ATCC 44860 a provoqué une faible mortalité des larves.相似文献
27.
Even Amler Nelvio Cester Eleonora Salvolini Roberto Staffolani Martin Burkhard Laura Mazzanti Arnot Kotyk Carlo Romanini 《Cell biology international》1994,18(7):723-727
Placentas of women suffering from pregnancy-induced hypertension (PIH) were found to contain a greater amount of Na,K-ATPase molecules, estimated from anthroyl ouabain binding, than normotensive individuals. Both the microsomal fraction of placental cells and purified Na,K-ATPase showed an increased affinity for the specific inhibitor ouabain which, in the case of the microsomes, bound with a dissociation constant of 0.9 nM as compared with 3.4 nM in the controls. Likewise, the dissociation constant of the ouabain complex with purified Na,K-ATPase was about 3.5 times lower in the hypertensive patients. The differences are apparently caused by a different microenvironment of the ouabain-binding site, as reflected in the quantum yield of bound anthroyl ouabain. If an endogenous digitalis-like factor is present in the body fluids to regulate Na,K-ATPase activity, the present results render its role quite plausible. 相似文献
28.
29.
OBJECTIVES: To determine the prevalence and risk indicators of cervical infection due to Chlamydia trachomatis among female patients consulting for contraception and to evaluate an enzyme immunoassay for the detection of C. trachomatis in this setting. DESIGN: Prevalence study. Endocervical specimens were analysed by means of culture and enzyme immunoassay. C. trachomatis infection was diagnosed through culture. SETTING: A hospital family planning clinic in Trois-Rivières, Que. SUBJECTS: All 533 female patients who consulted for contraception between November 1986 and March 1988. Results of culture were available for 495 patients. MAIN OUTCOME MEASURE: Demographic, epidemiologic and clinical information was collected by means of a standard questionnaire and a gynecologic examination. MAIN RESULTS: The prevalence rate of chlamydial infection was 9% (45/495). Enzyme immunoassay detected 37 (82%) of the infections. The mean age of the patients was 19.8 years, and 98% of the infections were diagnosed in those aged 25 years or less. The variables significantly associated with C. trachomatis infection were having more than one sexual partner in the preceding year (odds ratio [OR] 2.9; 95% confidence limits [CL] 1.7 and 5.0) and having more than one partner in the preceding 3 months (OR 2.3; 95% CL 1.2 and 4.3). These two indicators would have detected 58% and 22% of the infections respectively. CONCLUSIONS: Screening for C. trachomatis infection by means of enzyme immunoassay should be proposed to all female patients aged 25 years or less consulting for contraception in our clinic. Such screening may prove to be an effective preventive measure in other similar clinical settings. 相似文献
30.
Le Maître Anne Guy Franck Merceron Gildas Kostopoulos Dimitris S. 《International journal of primatology》2023,44(1):209-236
International Journal of Primatology - Discoveries in recent decades indicate that the large papionin monkeys Paradolipopithecus and Procynocephalus are key members of the Late Pliocene –... 相似文献