首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   59506篇
  免费   4952篇
  国内免费   5523篇
  2023年   721篇
  2022年   1008篇
  2021年   2772篇
  2020年   1965篇
  2019年   2543篇
  2018年   2609篇
  2017年   2150篇
  2016年   2748篇
  2015年   3308篇
  2014年   4212篇
  2013年   4502篇
  2012年   5191篇
  2011年   4837篇
  2010年   3368篇
  2009年   2962篇
  2008年   3417篇
  2007年   3069篇
  2006年   2695篇
  2005年   2230篇
  2004年   2053篇
  2003年   1883篇
  2002年   1573篇
  2001年   1219篇
  2000年   1019篇
  1999年   770篇
  1998年   493篇
  1997年   412篇
  1996年   370篇
  1995年   358篇
  1994年   340篇
  1993年   256篇
  1992年   335篇
  1991年   302篇
  1990年   258篇
  1989年   225篇
  1988年   147篇
  1987年   192篇
  1986年   175篇
  1985年   144篇
  1984年   118篇
  1983年   113篇
  1982年   93篇
  1981年   90篇
  1980年   59篇
  1979年   79篇
  1978年   72篇
  1977年   58篇
  1976年   59篇
  1975年   54篇
  1973年   68篇
排序方式: 共有10000条查询结果,搜索用时 156 毫秒
81.
82.
83.
The paper studies mycobiota of the dead insects in West Siberia, Primorsky krai, and Kyrgyzstan. Ascomycetes anamorphs of 13 genera are revealed. In all regions Beauveria bassiana (Bals.-Criv.) Vuill. dominated comprising on average 68% of the total number of isolates. The fungus hosts list the insects of 7 orders and 32 families with Coleoptera, Lepidoptera, and Hemiptera dominating. The rarely found entomopathogens include Tolypocladium inflatum Gams (primarily on Lepidoptera), Metarhizium anisopliae (Metschn.) Sorokin (on Coleoptera). The mortality rate of the insects due to micromycetes is observed mainly on enzootic level. The study of the pathogenic properties of the dominating species (B. bassiana) show the absence of specificity of its environmental isolates for a number of representatives of Orthoptera, Lepidoptera, Coleoptera, and Diptera.  相似文献   
84.
The paper presents the results of theoretical and experimental studies of the radiative properties of plasmas produced by heating and compression of various materials to high energy densities. The specific features of the theoretical plasma model known as the ion model, which is used to calculate the radiative characteristics of plasmas of complex chemical composition, are discussed. The theoretical approach based on this model is applied to the plasma produced during the explosion of the X-pinch wires. The theoretical estimate of the radiation efficiency is compared with the experimental data on the total energy yield from an X-pinch made of two different wires (NiCr and Alloy 188). The radiative characteristics of (C12 H16 O8) and (C8 H12 O6) plasmas are calculated for the temperature diagnostics of plasmas produced from porous targets employed in inertial confinement fusion experiments with the use of laser radiation and heavy-ion beams.  相似文献   
85.
A neutral cholesterol esterase has been purified to homogeneity from the cytosolic fraction of rat liver. The 105,000 x g supernatant fraction of rat liver was applied to a DEAE-cellulose column to isolate a partially purified fraction of hepatic cholesterol esterase. Immunoblot analysis of the partially purified liver fraction with the anti-porcine pancreatic cholesterol esterase IgG demonstrated a single band with a molecular weight of 67,000. The hepatic protein was then isolated by immunoaffinity chromatography technique using a column constructed with antibodies prepared against the pancreatic cholesterol esterase. Characterization of the hepatic cholesterol esterase revealed that the hepatic enzyme shared antigenic epitopes with the pancreatic cholesterol esterase and was similarly activated by addition of bile salt such as taurocholate. Moreover, amino-terminal sequencing analysis of the hepatic cholesterol esterase showed an identical sequence with the pancreatic enzyme. Taken together, these results showed that the cholesterol esterases in the liver and the pancreas are very similar and possibly identical proteins.  相似文献   
86.
A simple and rapid method is described for the purification of supercoiled PM2 DNA by affinity chromatography on columns of H1 histone covalently coupled to agarose. The method does not require the use of intercalating agents or ultracentrifugation procedures. Under the conditions most appropriate for purification, elution is carried out in a single step with buffered 0.7 M NaCl after the sample has been loaded onto the column in buffered 0.2 M NaCl. The DNA eluted at the higher salt concentration consists of supercoiled closed circular DNA at greater than 90% purity independently of the ratio of supercoiled to nicked circular DNA in the input mixture.  相似文献   
87.
Directly observed 15N NMR spectra of uniformly enriched proteins   总被引:1,自引:0,他引:1  
G M Smith  L P Yu  D J Domingues 《Biochemistry》1987,26(8):2202-2207
The proteins cytochrome c2, cytochrome c', and ribulosebisphosphate carboxylase/oxygenase from Rhodospirillum rubrum were enriched in 15N by growth of the organism on 15NH4Cl. The proteins were purified to homogeneity and studied by 15N NMR. Longitudinal and transverse relaxation times as well as the nuclear Overhauser effects were determined for various groups of the proteins which vary in molecular weight from 13,000 to 114,000. The values of these parameters for the amide resonances or for groups thought to be rigid were consistent with the molecular weights of the proteins. Relaxation times of the amino-terminal alpha-amino groups and the side chain nitrogen atoms of arginine and lysine were consistent with much more rapid motion. Nitrogen atoms having bound protons were generally found to be decoupled from the protons by chemical exchange. Demonstrable 1H-15N coupling was taken as an indication that exchange was hindered, either by hydrogen bonding interactions or by inaccessibility of the group to solvent. Histidine side chain nitrogen atoms, which experience a large chemical shift upon protonation/deprotonation, were often found to be broadened beyond detectability by chemical exchange and tautomerization. Strategies for improving sensitivity and for obtaining specific peak assignments are also discussed.  相似文献   
88.
Plasma Physics Reports - It is shown theoretically that under the effect of plasma flows typical of transient processes in tokamaks not only can Kelvin–Helmholtz instability develop and waves...  相似文献   
89.
Species composition and ecological structure of ground beetle population was studied in northern taiga meadows of the Arkhangelsk Region. Meadows in the northern forest zone proved to harbor 91 ground beetle species. Carabid complexes formed in the intrazonal biocenoses of the northern forest zone can be as rich as the family topical groups in the southern forest zone by the number of species and ecological diversity. Ecological properties of the fauna and ground beetle population proved similar in different parts of the forest zone. The proportion of stenobiotic meadow species proved to decrease while that of ecologically plastic ones increased from south to north. The proportion of the genus Harpalus decreased in the ground beetle population while the number of Amara species remained unaltered and their abundance increased. The changes in the species composition caused no transformation of the ecological structure of ground beetle population since they were limited to a single life form or guild.  相似文献   
90.
Natural heparin complexes proved to activate the anticoagulation system. The obtained experimental data convincingly confirm that glutamic acid alone, and particularly in a complex with heparin, has a considerable preventive potential and efficiently protects experimental animals with induced diabetes mellitus.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号