全文获取类型
收费全文 | 7256篇 |
免费 | 163篇 |
国内免费 | 605篇 |
专业分类
8024篇 |
出版年
2022年 | 30篇 |
2021年 | 37篇 |
2018年 | 445篇 |
2017年 | 351篇 |
2016年 | 186篇 |
2015年 | 160篇 |
2014年 | 102篇 |
2013年 | 148篇 |
2012年 | 170篇 |
2011年 | 536篇 |
2010年 | 380篇 |
2009年 | 139篇 |
2008年 | 200篇 |
2007年 | 108篇 |
2006年 | 66篇 |
2005年 | 319篇 |
2004年 | 560篇 |
2003年 | 285篇 |
2002年 | 194篇 |
2001年 | 278篇 |
2000年 | 121篇 |
1999年 | 157篇 |
1998年 | 79篇 |
1997年 | 140篇 |
1996年 | 89篇 |
1995年 | 100篇 |
1994年 | 42篇 |
1993年 | 361篇 |
1992年 | 335篇 |
1991年 | 220篇 |
1990年 | 161篇 |
1989年 | 175篇 |
1988年 | 161篇 |
1987年 | 133篇 |
1986年 | 120篇 |
1985年 | 148篇 |
1984年 | 63篇 |
1983年 | 35篇 |
1979年 | 35篇 |
1978年 | 22篇 |
1977年 | 23篇 |
1975年 | 51篇 |
1974年 | 43篇 |
1973年 | 35篇 |
1972年 | 32篇 |
1971年 | 40篇 |
1970年 | 32篇 |
1968年 | 23篇 |
1966年 | 24篇 |
1965年 | 22篇 |
排序方式: 共有8024条查询结果,搜索用时 0 毫秒
991.
992.
993.
Keith W.T.Goulding 《中国科学:生命科学英文版》2005,48(Z2)
The nitrogen (N) cycle is essentially 'leaky'. The losses of small amounts of nitrate to waters and of ammonia and nitrous oxide to the atmosphere are a part of the global biogeo-chemical N cycle. However, intensive agricultural production, industry and vehicle use have more than doubled the amount of 'reactive' N in the environment, resulting in eutrophication, ecosystem change and health concerns. Research has identified agricultural practices that cause large losses of N and, in some cases, developed solutions. This paper discusses the problems of maintaining productivity while reducing N losses, compares conventional with low input (integrated) and organic farming systems, and discusses wider options. It also looks at the need to integrate studies on N with other environmental impacts, set in the context of the whole farm system, to provide truly sustainable agricultural systems. 相似文献
994.
995.
S G Yevdokimov YuMSkuridin V I Salyanov G Damaschun H Damaschun R Misselwitz V Kleinw?chter 《Biophysical chemistry》1990,35(2-3):143-153
We have investigated the X-ray and optical properties (CD spectra and polarization microscopy) of liquid-crystalline phases and dispersions formed on pretreatment of low molecular weight DNA with the platinum(II) coordination complexes, cis-diammine-dichloroplatinum(II) (DDP), 2,2'-bipyridinedichloroplatinum(II) (1) and 2,2'-bipyridineethylenediammineplatinum(II) (2). It is demonstrated that the platination of DNA leads to the ordering of neighbouring molecules of DNA in liquid-crystalline phases being diminished. The intense bands observed in the CD spectra of liquid-crystalline dispersions prepared from DNA pretreated with 1 or 2 can be used to determine the orientation of the latter compounds with respect to the helical axis of the DNA and to detect distortions in the secondary structure of DNA. The possible causes of the appearance of the intense bands in the CD spectra of liquid-crystalline phases and alterations in the manner of packing of the molecules of DNA within them are discussed. 相似文献
996.
Li-Qing XIAO Ai-Hua LIU and Yong-Lian ZHANG State Key Laboratory of Molecular Biology Institute of Biochemistry Cell Biology Shanghai Institutes for Biological Sciences Chinese Academy of Sciences Graduate School of the Chinese Academy of Sciences Shanghai China 《Acta biochimica et biophysica Sinica》2004,(8)
Defensins are a family of evolutionarily relatedvertebrate antimicrobial peptides with a characteristicβ-sheet-rich fold and a framework of six disulphide-linkedcysteines. The two main defensin subfamilies, α- andβ-defensin, differ in the length of pep… 相似文献
997.
Wenyi Yan a bc Shenghai Ye b Qingsheng Jin b Longjun Zeng c Yu Peng c Dawei Yan c Weibing Yang c Donglei Yang c Zuhua He c Yanjun Dong a Xiaoming Zhang b a College of Life Environment Sciences Shanghai Normal University Shanghai China b Institute of Crop Nuclear Technology Utilization Zhejiang Academy of Agricultural Sciences Hangzhou China c Institute of Plant Physiology & Ecology Shanghai Institutes for Biological Sciences Chinese Academy of Sciences Shanghai China 《Acta Genetica Sinica》2010,(1)
Plant senescence plays diverse important roles in development and environmental responses.However,the molecular basis of plant senescence is remained largely unknown.A rice spontaneous mutant with the character of early senescence and male sterility (sms) was found in the breeding line NT10-748.In order to identify the gene SMS1 and the underlying mechanism,we preliminarily analyzed physiological and biochemical phenotypes of the mutant.The mutant contained lower chlorophyll content compared with the wild t... 相似文献
998.
1000.
Light is essential for root gravitropism in Zea mays L., cultivar Merit. It is hypothesized that calcium mediates this light-regulated response. KN-93, an inhibitor of calcium/calmodulin kinase II (CaMK II), inhibits light-regulated root gravitropism but does not affect light perception. We hypothesize that CaMK II, or a homologue, operates late in the light/gravity signal transduction chain. Here we provide evidence suggesting a possible physiological involvement of CaMK II in root gravitropism in plants. 相似文献