全文获取类型
收费全文 | 39260篇 |
免费 | 2810篇 |
国内免费 | 5242篇 |
专业分类
47312篇 |
出版年
2024年 | 193篇 |
2023年 | 809篇 |
2022年 | 1068篇 |
2021年 | 1300篇 |
2020年 | 1265篇 |
2019年 | 1876篇 |
2018年 | 1542篇 |
2017年 | 1263篇 |
2016年 | 1210篇 |
2015年 | 1194篇 |
2014年 | 1899篇 |
2013年 | 2705篇 |
2012年 | 1552篇 |
2011年 | 1740篇 |
2010年 | 1377篇 |
2009年 | 1773篇 |
2008年 | 1775篇 |
2007年 | 1959篇 |
2006年 | 1735篇 |
2005年 | 1599篇 |
2004年 | 1379篇 |
2003年 | 1336篇 |
2002年 | 1209篇 |
2001年 | 923篇 |
2000年 | 858篇 |
1999年 | 772篇 |
1998年 | 765篇 |
1997年 | 661篇 |
1996年 | 561篇 |
1995年 | 559篇 |
1994年 | 537篇 |
1993年 | 492篇 |
1992年 | 461篇 |
1991年 | 491篇 |
1990年 | 370篇 |
1989年 | 392篇 |
1988年 | 373篇 |
1987年 | 314篇 |
1986年 | 351篇 |
1985年 | 551篇 |
1984年 | 640篇 |
1983年 | 357篇 |
1982年 | 497篇 |
1981年 | 497篇 |
1980年 | 425篇 |
1979年 | 316篇 |
1978年 | 230篇 |
1977年 | 240篇 |
1976年 | 236篇 |
1973年 | 185篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
J.G. Roddick 《Phytochemistry》1974,13(1):9-25
The literature relating to chemical, biochemical and biological aspects of the steroidal glycoalkaloid, α-tomatine, is reviewed. The alkaloid, which can be used as a starting compound for the synthesis of steroidal hormones, is toxic to a wide range of living organisms. The significance of tomatine to plants which elaborate it is discussed and some possible uses of the compound are mentioned. 相似文献
2.
3.
Papers on the mechanisms of translation initiation in mammals studied by reconstruction of initiation complexes from individual components are reviewed. The author points to the constraints of this approach and to the pitfalls ignoring which one might come to erroneous conclusions and even artifacts. In addition, some methods employed in the field as well as some technical problems are discussed in the paper, together with the means of obviating them. The review could be a guidebook for newcomers into this quite labor-consuming field. 相似文献
4.
Complementarity of regulation for the two glutamine synthetases from Bacillus caldolyticus, an extreme thermophile 总被引:1,自引:0,他引:1
F C Wedler D S Shreve K E Fisher D J Merkler 《Archives of biochemistry and biophysics》1981,211(1):276-287
Chromatophores from Rhodopseudomonas capsulata cells grown semiaerobically in the dark oxidize NADH, succinate, and dichlorophenolindophenol. In the presence of N3? these activities are inhibited, but light induces oxidation of dichlorophenolindophenol with O2 as a terminal electron acceptor. Cyanide also inhibits electron transport but much higher concentrations are required to inhibit the photooxidation than the dark oxidation. The photooxidation was studied in a mutant strain of Rhodopseudomonas capsulata (YIV) which cannot grow anaerobically in the light, but similarly to the wild type, grows in the presence of oxygen. Chromatophores from YIV mutant catalyze photophosphorylation and dark oxidation activities with the same properties as those of the wild type. However, the rate of photooxidation in the mutant is only one-third that of the wild type. Based on the differential inhibitor sensitivity and on the mutation it is suggested that the photooxidase is different from the two respiratory oxidases and that this photooxidation activity might be essential for growth of the cells under anaerobic conditions in the light. 相似文献
5.
6.
T. J. Wojciechowski 《Biometrical journal. Biometrische Zeitschrift》1987,29(8):953-959
In this paper very simple nonparametric classification rule for mixtures of discrete and continuous random variables is described. It is based on the method of nearest neighbor proposed by Cover and Hart (1967). The bounds on the limit of the nearest neighbor rule risks are given. Both lower and upper bound depend on the Bayes risk and the loss function. Finally the method is compared with other existing methods on some practical data set. 相似文献
7.
8.
9.
S. L. GLOCKLING FLS G. W. BEAKES 《Botanical journal of the Linnean Society. Linnean Society of London》2001,136(3):329-338
Two new species of Haptoglossa , one zoosporic, H. northumbrica , and one aplanosporic, H. polymorphs, , were isolated from samples of manure and horse dung in north-east England. The zoosporic H. northumbrica is morphologically similar to H. dickii but differs in having slightly smaller infection gun cells with a unique internal arrangement of cones in the apical missile chamber. The thallus of the aplanosporic H. polymorpha is similar to H. heteromorpha but produces three different types of aplanospore. The smaller cysts either develop into broad, arcuate gun cells or form curved adhesive cells that have a rounded base. These curved adhesive cells have very different internal ultrastructural organization. The large cysts develop into infection cells that are morphologically similar to the curved adhesive cells, but their internal structure has not yet been observed. 相似文献
10.
Several unit-length minicircles from the kinetoplast DNA of Leishmania tarentolae were cloned into pBR322 and into M13 phage vectors. The complete nucleotide sequences of three different partially homologous minicircles were obtained. The molecules contained a region of approx. 80% sequence homology extending for 160–270 bp and a region unique to each minicircle. A 14-mer was found to be conserved in all kinetoplast minicircle sequences reported to date. The frequency distributions of various minicircle sequence classes in L. tarentolae were obtained by quantitative gel electrophoresis and by examination of the “T ladder” patterns of minicircles randomly cloned into M13 at several sites. By these methods we could assign approx. 50% of the total minicircle DNA into a minimum of five sequence classes. A sequence-dependent polyacrylamide gel migration abnormality was observed with several minicircle fragments both cloned and uncloned. The abnormality was dependent on the presence of a portion of the conserved region of the minicircle. 相似文献