全文获取类型
收费全文 | 226673篇 |
免费 | 15286篇 |
国内免费 | 49篇 |
专业分类
242008篇 |
出版年
2021年 | 1819篇 |
2018年 | 3211篇 |
2017年 | 3094篇 |
2016年 | 3747篇 |
2015年 | 3339篇 |
2014年 | 4571篇 |
2013年 | 6494篇 |
2012年 | 7721篇 |
2011年 | 8234篇 |
2010年 | 5851篇 |
2009年 | 4973篇 |
2008年 | 7348篇 |
2007年 | 7601篇 |
2006年 | 7301篇 |
2005年 | 6817篇 |
2004年 | 6955篇 |
2003年 | 6671篇 |
2002年 | 6623篇 |
2001年 | 9352篇 |
2000年 | 9020篇 |
1999年 | 7044篇 |
1998年 | 2154篇 |
1997年 | 1980篇 |
1996年 | 1843篇 |
1992年 | 5506篇 |
1991年 | 5715篇 |
1990年 | 5683篇 |
1989年 | 5649篇 |
1988年 | 5241篇 |
1987年 | 4888篇 |
1986年 | 4487篇 |
1985年 | 4701篇 |
1984年 | 3715篇 |
1983年 | 3042篇 |
1982年 | 2024篇 |
1981年 | 1730篇 |
1980年 | 1733篇 |
1979年 | 3350篇 |
1978年 | 2591篇 |
1977年 | 2380篇 |
1976年 | 2334篇 |
1975年 | 2833篇 |
1974年 | 3128篇 |
1973年 | 3102篇 |
1972年 | 2749篇 |
1971年 | 2607篇 |
1970年 | 2213篇 |
1969年 | 2164篇 |
1968年 | 2034篇 |
1967年 | 1799篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
871.
Yu. S. Ravkin S. M. Tsybulin S. G. Livanov K. V. Toropov V. N. Kuranova V. P. Starikov S. V. Chesnokova 《Contemporary Problems of Ecology》2008,1(5):568-573
For the entire territory of West Siberia, including its plain and mountainous parts, two maps were constructed for populations of amphibians together with reptiles, and of birds. Communities of these classes of vertebrates differ from one another in their spatial differentiation. The differences are demonstrated for the plain and mountainous territories considered jointly and separately. 相似文献
872.
873.
874.
Self-association of human erythrocyte glycophorin A. Appearance of low mobility bands on sodium dodecyl sulfate gels 总被引:2,自引:0,他引:2
We have examined the self-association of glycophorin A, the major sialoglycoprotein of the human erythrocyte membrane, using sodium dodecyl sulfate (SDS) polyacrylamide gels and circular dichroism. Pure glycophorin A has a tendency to form multiple bands on SDS gels at positions of higher apparent molecular weight than the PAS 1 and PAS 2 bands previously seen. These high molecular weight bands do not have mobilities corresponding to integral polymers of PAS 1 and PAS 2. Circular dichroism spectra of solutions giving rise to these bands or to PAS 1 and PAS 2 bands alone, indicate that these species all have essentially the same peptide conformation. 相似文献
875.
The action of new beta-blockers of VUFB series (VUFB 6502, VUFB 8102, VUFB 8227, and trimepranol) (Fig. 1) was analyzed in smooth msucle of guinea pig taenia coli by the double sucrose-gap method. All the studied beta-blockers increased the spontaneous spike activity without changes in membrane potential. The amino-analogues (VUFB 8101, VUFB 8102, VUFB 8227) as well as practolol were found to be 50 to 100 times less active than the oxy-derivatives (VUFB 6502 and Trimepranol) for the inhibition of spike activity, muscle relaxation and membrane hyperpolarization evoked by isoprenaline. None of the studied compounds had a pronounced alpha-blocking activity. The structure-activity relationship of the studied compounds was discussed. 相似文献
876.
877.
Nucleotide sequence of the EcoRII restriction endonuclease gene 总被引:3,自引:0,他引:3
The nucleotide sequence of a 1394 basepair (bp) DNA fragment containing the EcoRII restriction endonuclease (R.EcoRII) gene was determined. The endonuclease gene is 1206 bp in length (predicted 402 amino acids (aa) and Mr = 45 178) and is separated by 33 bp from the EcoRII modification methylase (M.EcoRII) gene. The EcoRII restriction-modification system has a tail-to-tail organization of the two genes. 相似文献
878.
Abstract— —Adult rat brain nuclei were separated by discontinuous sucrose gradient centrifugation into astrocyte enriched, neuron enriched, and oligodendrocyte/microglia fractions. Nuclear fractions were subjected to velocity sucrose gradient centrifugation and gradient fractions assayed using relatively specific reaction mixtures for DNA polymerase-α, -β and TdT. NEM resistant DNA polymerase activity (DNA polymerase-β) was detected in equivalent amounts in all nuclear fractions. High molecular weight NEM sensitive activity (DNA polymerase-α) was found primarily in the neuron enriched fraction. The significance of the presence of DNA polymerase-α, an enzyme thought to be involved in DNA replication, in a cell incapable of cell division is unknown. TdT was detected in all fractions with increased activity in the neuron enriched fraction. The finding of TdT in thymocytes and neurons further supports the hypothesis that this enzyme is involved in the storage of noninherited information. 相似文献
879.
B I Marakusha V G Petrovskaia K I Volkovo? 《Zhurnal mikrobiologii, epidemiologii, i immunobiologii》1986,(10):3-8
Mutants, resistant to neamine and spectinomycin, have been isolated from S. typhimurium and S. dublin highly virulent strains. The neamine-resistant mutants can be divided into 3 classes in accordance with their sensitivity to streptomycin: sensitive, resistant to low and high concentrations of this antibiotic. The transduction analysis with the use of bacteriophage P 22 has revealed that the spectinomycin-resistant mutations under study are spc A mutations, while the mutations leading to resistance to neamine in class Near Strr 500 are nea B mutations. The mutation leading to resistance to spectinomycin (spc A) has been found to produce no changes in the virulence of salmonellae in the intraperitoneal infection of mice. The mutations leading to resistance to neamine and streptomycin (nea B and str A) have been found to decrease virulence. 相似文献
880.
A I Vengerovski? V S Chuchalin O V Paul's A S Saratikov 《Biulleten' eksperimental'no? biologii i meditsiny》1987,103(4):430-432
The hepatoprotective agents, silybinin and essentiale, were shown to prevent the development of lipid metabolism disturbances in the liver and serum of rats with CCl4-hepatitis. Slow accumulation of triglycerides, lysophosphatidylcholine and cardiolipin was observed in animals treated with these drugs, while phosphatidylcholine liver level remained high. Silybinin and essentiale inhibited the production of lipid hydroperoxide, Shiff basis, malonic dialdehyde, intensified the function of tissue antioxidants, activated liver beta-hydroxybutyrate dehydrogenase and depressed the activation of serum phospholipase A. 相似文献