全文获取类型
收费全文 | 27089篇 |
免费 | 2367篇 |
国内免费 | 3382篇 |
出版年
2024年 | 40篇 |
2023年 | 275篇 |
2022年 | 431篇 |
2021年 | 1352篇 |
2020年 | 979篇 |
2019年 | 1227篇 |
2018年 | 1145篇 |
2017年 | 826篇 |
2016年 | 1146篇 |
2015年 | 1737篇 |
2014年 | 2038篇 |
2013年 | 2097篇 |
2012年 | 2637篇 |
2011年 | 2349篇 |
2010年 | 1482篇 |
2009年 | 1355篇 |
2008年 | 1575篇 |
2007年 | 1432篇 |
2006年 | 1319篇 |
2005年 | 1198篇 |
2004年 | 961篇 |
2003年 | 947篇 |
2002年 | 727篇 |
2001年 | 502篇 |
2000年 | 454篇 |
1999年 | 466篇 |
1998年 | 280篇 |
1997年 | 259篇 |
1996年 | 259篇 |
1995年 | 192篇 |
1994年 | 215篇 |
1993年 | 134篇 |
1992年 | 150篇 |
1991年 | 140篇 |
1990年 | 98篇 |
1989年 | 90篇 |
1988年 | 58篇 |
1987年 | 63篇 |
1986年 | 47篇 |
1985年 | 43篇 |
1984年 | 44篇 |
1983年 | 25篇 |
1982年 | 18篇 |
1981年 | 10篇 |
1979年 | 4篇 |
1978年 | 3篇 |
1971年 | 2篇 |
1966年 | 1篇 |
1953年 | 1篇 |
1950年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 78 毫秒
91.
兔的一种新病毒:Ⅱ.一株兔出血症... 总被引:4,自引:1,他引:3
In this paper a strain of Rabbit Hemorrhagic Disease Virus (RHDV) was isolated and purified from the diseased rabbit livers with a method of using chloroform, two-phase of polyethylene-glycol-dextran sulfate sodium and sucrose density gradient centrifugation. Purified virus was nonenveloped, icosahedeal symmetry with a triangulation number of 3, and 33-37 nm in diameter. The capsid was composed of 32 capsomeres with central holes in an outer diameter of about 9nm. Two types of viral particles having different sedimentation coefficient, 130s and 166s could be identified after sucrose density gradient centrifugation. Probably no less than four virion proteins with molecular weight of 66.4, 65.0, 63.5, 41.0 x 10(3) dalton were detected by SDS-polyacrylamide gel electrophoresis. Viral nucleic acid was extracted from purified virus by using SDS-proteinase K-phenol. Tests with diphenylamine, formaldehyde, and staining with acridine orange as well as the curves of thermal denaturation showed that this kind of virus had a single-stranded DNA. The molecular weight of the ssDNA was approx 2.1 x 10(6) dalton as determined by electron microscopy. Data indicate that the RHDV may like the parvovirus of the family Parvoviridae. 相似文献
92.
A stable xylan suspension was prepared and characterized. Hydrolysis of the particles converts them into soluble fragments, thereby lowering the turbidity of the suspension. The small volume of the assay mixture, the short incubation time required, and the simplicity of the procedure permit the rapid analysis of many samples. Furthermore, the procedure can be used to assay xylanase activities in the presence of other reducing materials and is also useful for monitoring low-level xylanase activities. 相似文献
93.
Fibrinogen Lille, a congenital dysfibrinogenemia, has been reported to arise from a mutation from Asp to Asn at position 7 of the A alpha chain of human fibrinogen, thereby reducing the thrombin-catalyzed rate of hydrolysis of the Arg(16)-Gly(17) peptide bond of this chain. Synthetic peptides of relevant portions of the wild-type and mutant A alpha chains were prepared, and the thrombin-catalyzed rates of hydrolysis of their Arg(16)-Gly(17) peptide bonds were determined. In addition, transferred NOE measurements were made to deduce their conformations, when complexed to bovine thrombin. The kinetics data showed little difference in the hydrolysis rates between the wild-type and mutant peptides, and the NMR data indicate no difference in the bound conformation of these two peptides. Therefore, electrostatic (or salt-bridge) interactions between Asp(7) and thrombin do not influence the bound conformations of these peptides. Asp(7) may interact with a remote residue of fibrinogen, not present in these synthetic peptides, or there may be additional mutations beyond A alpha (1-20) which have not been detected in fibrinogen Lille. Alternatively, when thrombin binds to fibrinogen at its secondary binding site, its primary (active) site may display different reactivities toward wild-type fibrinogen and fibrinogen Lille. 相似文献
94.
Shu-Yu Yu Bao-Lin Mao Ping Xiao Wei-Ping Yu Ying-Long Wang Chang-Zhi Huang Wang-Qiu Chen Xiang-Zhan Xuan 《Biological trace element research》1990,24(2-3):105-108
This pilot study evaluated the feasibility and effectiveness of conducting a double-blind clinical trial for the prevention of lung cancer with selenium (Se) in Yunnan Tin Corporation, the People's Republic of China, where the incidence rates of lung cancer are extraordinarily high among the miners. Forty healthy miners were randomized to either 300 μg of Se in high Se malt cakes or an identical placebo of malt cakes daily for one year. Subjects consumed their usual daily diet. The low Se concentrations in plasma (0.05±0.008 μg/mL) and hair (0.442±0.085 μg/g) reflected their low dietary Se intake in the control subjects. In Se-supplemented group, the Se status was increased by 178% for serum and 194.8% for hair. The serum GSHpx activity was increased by 155.7%, whereas the lipid peroxide level was reduced by 74.5% compared to the placebo. The results of UDS assay indicated that the lymphocyte DNA damage induced by ultraviolet irradiation and carcinogen 3,4-benzpyrene could be protected by Se supplementation. Se-supplementation did not affect the liver function test (SGPT), as well as the concentrations of hemoglobin, albumin, and cholesterol. Thus, daily intake of 300 μg Se in form of Se-malt as a chemopreventive measure is safe and effective to humans with low Se status. 相似文献
95.
We have studied the properties of kainic acid receptor-activated channels using domoic acid as an agonist. Similarities of the electrophysiological, pharmacological and noise properties of domoic acid and kainic acid-evoked currents confirm that domoate is a potent and specific agonist of the kainate receptor. Single-channel properties of domoic acid-evoked currents were directly determined from outside-out membrane patches for the first time, and results were compared with those obtained by fluctuation analysis of macroscopic currents. Small conductance cationic-selective channels of 4 pS and a mean open time of 2 to 3 ms were detected using both methods.
Offprint requests to: O. Moran 相似文献
96.
97.
季节及人工低温对大蟾蜍肌组织ATP酶的影响研究 总被引:1,自引:0,他引:1
本文研究了大蟾蜍心肌和腓肠肌肌球蛋白钙激活ATP酶的活性。实验结果显示,大蟾蜍心肌和腓肠肌肌球蛋白钙激话ATP酶活性具有不同的季节变化规律。并且这种酶活性的季节变化不受人工低温环境因素的影响。此外,大蜍蟾心肌中ATP酶的活性始终高于腓肠肌的。上述酶活性的变化均具有一定的生理意义。 相似文献
98.
水葫芦根部分泌物对若干细菌作用的研究 总被引:13,自引:1,他引:12
生态系统中各种生物种群之间的关系是错综复杂的,而物种之间的关系又直接或间接地影响着生态系统的功能。水葫芦对藻类的克制效应,以及城市富营养化水域的生物治理 相似文献
99.
植物群落演替与土壤发展之间的关系 总被引:46,自引:0,他引:46
张全发;郑重;金义兴 《武汉植物学研究》1990,8(4):325-334
本文运用植物群落中植物优势种的重要值与相对应子群落的土壤特征值直接相关联的分析方法,对湖北宜昌大老岭的桦(Betula)、栎(Quercus)、栗(Castanea)七个群落类型的三个演替途径的土壤动态进行分析,结果表明:在植物群落的演替过程中,土壤中的Ca、pH值减少;离子代换量增加;Na、Mg、NH_4+-N、速效P、速效K、有机质的含量是随着物种的变化而呈不同的趋势。因此,植物群落的演替是生态系统的动态过程。 相似文献
100.
浙江珍稀濒危保护植物的地理分布及其区系特征 总被引:13,自引:0,他引:13
本文分析了浙江珍稀濒危保护植物56种的地理分布和51属的分布区类型及其区系特征,其结果如下: 1.本区存在较多的我国特有属,单型属、少型属的事实,说明浙江省的珍稀濒危植物区系的古老性和相对原始性。2.根据51属的分布区类型的分析,其属具有明显的温带性质,而56种的地理分布则以亚热带区系成分为主,它们与华中亚热带区系植物关系密切。 相似文献