全文获取类型
收费全文 | 788071篇 |
免费 | 88903篇 |
国内免费 | 893篇 |
专业分类
877867篇 |
出版年
2018年 | 7255篇 |
2016年 | 9896篇 |
2015年 | 13762篇 |
2014年 | 16171篇 |
2013年 | 22179篇 |
2012年 | 25575篇 |
2011年 | 26333篇 |
2010年 | 17820篇 |
2009年 | 16323篇 |
2008年 | 23588篇 |
2007年 | 24497篇 |
2006年 | 23055篇 |
2005年 | 21878篇 |
2004年 | 21992篇 |
2003年 | 20631篇 |
2002年 | 20155篇 |
2001年 | 31763篇 |
2000年 | 31924篇 |
1999年 | 25519篇 |
1998年 | 9657篇 |
1997年 | 9813篇 |
1996年 | 9273篇 |
1995年 | 8856篇 |
1994年 | 8448篇 |
1993年 | 8559篇 |
1992年 | 21460篇 |
1991年 | 21326篇 |
1990年 | 20790篇 |
1989年 | 20114篇 |
1988年 | 19089篇 |
1987年 | 18088篇 |
1986年 | 17054篇 |
1985年 | 16788篇 |
1984年 | 14059篇 |
1983年 | 12255篇 |
1982年 | 9409篇 |
1981年 | 8468篇 |
1980年 | 7984篇 |
1979年 | 13356篇 |
1978年 | 10769篇 |
1977年 | 9713篇 |
1976年 | 9277篇 |
1975年 | 10335篇 |
1974年 | 11477篇 |
1973年 | 11239篇 |
1972年 | 10237篇 |
1971年 | 9439篇 |
1970年 | 8170篇 |
1969年 | 8073篇 |
1968年 | 7561篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
261.
G A Vilkov E M Stepanenko T A Khoruzhaia 《Biulleten' eksperimental'no? biologii i meditsiny》1985,99(1):48-50
The authors studies the effects of blood serum and IgG fraction from dogs immunized with brain and blood sera from patients with multiple sclerosis and schizophrenia on lipid peroxidation in rat brain homogenates. Measured the content of diene conjugates (DC) and malonic dialdehyde (MDA) in the rat brain after administering the IgG fraction. It was established that antioxidant activity of blood sera and IgG fraction from control animals and donors was significantly higher as compared to experimental. Administration of the IgG fraction brought about an increase in the content of DC and MDA in the brain of experimental animals. It is concluded that complement-dependent brain antibodies present in the blood serum of patients with schizophrenia and multiple sclerosis potentiate lipid peroxidation in the cerebral tissue and that the unsophisticated and informative method for antibody determination may be used in clinical practice. 相似文献
262.
M Sj?lund J Nilsson L Palmberg J Thyberg 《Differentiation; research in biological diversity》1984,27(2):158-162
The effects of prostaglandin E1 (PGE1) on the phenotypic state of enzymatically isolated arterial smooth-muscle cells in primary culture were studied by transmission electron microscopy, thymidine autoradiography, and cell counting. Early in culture (day 0-2), PGE1 stimulated conversion of the cells from contractile (less euchromatic nucleus and cytoplasm dominated by myofilament bundles) to synthetic state (more euchromatic nucleus and cytoplasm dominated by cisternae of rough endoplasmic reticulum and a large Golgi complex). The rate of entrance of the cells into DNA synthesis and mitosis was also increased at this time. Later on (day 3-6), when the majority of the cells had entered synthetic state, PGE1 inhibited DNA synthesis and cellular proliferation. These observations indicate that the effect of prostaglandins on arterial smooth muscle is dual in nature and dependent on the state of differentiation of the cells. 相似文献
263.
264.
In C4 plants phosphoenolpyruvate (PEP) of the C4 cycle may betransported on a chloroplast transporter which also transports3-phosphoglycerate (3-PGA) and triosephosphates. In C3 plantsPEP is not considered to be effectively transported on the chloroplastphosphate translocator. The influences of certain organic phosphates,having a similar structure to either PEP or triose-phosphates,on 3-PGA dependent O2 evolution by C4 (Digitaria sanquinalisL. Scop.) and C3 (Hordeum vulgare L.) mesophyll chloroplastswere investigated. In the C4 mesophyll chloroplasts phosphoglycolatewas a competitive inhibitor (Ki = 2.1 mM) of 3-PGA dependentO2 evolution, and was as effective as previously reported forPEP. 2-Phosphoglycerate was also a competitive inhibitor (Kt= 8.6 mM) of O2 evolution in the C4 mesophyll chloroplasts with3-PGA as substrate, while phospholactate was a weak inhibitorand glyphosate had no effect. Neither PEP, phosphoglycolatenor 2-phosphoglycerate were effective inhibitors of 3- PGA dependentO2 evolution in the C3 chloroplasts. Phosphohydroxypyruvatewas a competitive inhibitor of 3-PGA dependent O22 evolutionin both chloroplast types. The selectivity in inhibition ofO2 evolution with 3-PGA as substrate suggests that the C4 mesophyllchloroplasts can recognize certain organic phosphates with thephosphate in the C-2 or C-3 position but that the C4 mesophyllchloroplasts can only effectively recognize certain organicphosphates with the phosphate in the C-3 position. The resultsalso support the view that 3-PGA and PEP are transported onthe same phosphate translocator in C4 mesophyll chloroplasts.
1 Current address: Department of Horticulture, 2001 Fyffe Court,The Ohio State University, Columbus, Ohio 43210-1096. (Received March 24, 1987; Accepted April 16, 1987) 相似文献
265.
266.
267.
268.
Ia I Serkiz A I Lipskaia L B Pinchuk V V Trishin Iu F Kataevski? G N Koval' 《Radiobiologiia》1991,31(5):629-634
Irradiation conditions in which laboratory animals were kept in experimental laboratories of Chernobyl and Kiev after the accident at the Chernobyl A.P.S. are described. The data are presented on the spectral structural and activity of radionuclides in the diet as well as in the organs and tissues of the animals. The radiation loads have been estimated with regard to an external gamma component and the internal one contributed by the incorporated radionuclides. It has been shown that radiation doses received by the animals during their lifetime due to these contributions do not exceed units of cGy. 相似文献
269.
V Ia Gotlib I I Pelevina E F Konoplia A A Al'ferovich A A Konradov 《Radiobiologiia》1991,31(3):318-325
On the basis of their own data and the literature the authors have analyzed the mechanism of biological action of low-level radiation on cells. In studying the harmful effect of gamma-radiation (10-40 cGy) on HeLa cells it was shown that damages occurred in 12 postirradiation generations. Analysis of cell distribution within the colonies has demonstrated that the share of colonies with low cell content and the number of giant cell increase. These data indicate that low-level radiation causes reproductive cell death that can occur not immediately but in later generations. 相似文献
270.