全文获取类型
收费全文 | 13385篇 |
免费 | 731篇 |
国内免费 | 3篇 |
专业分类
14119篇 |
出版年
2022年 | 64篇 |
2021年 | 146篇 |
2020年 | 92篇 |
2019年 | 119篇 |
2018年 | 172篇 |
2017年 | 160篇 |
2016年 | 260篇 |
2015年 | 406篇 |
2014年 | 488篇 |
2013年 | 926篇 |
2012年 | 870篇 |
2011年 | 871篇 |
2010年 | 559篇 |
2009年 | 526篇 |
2008年 | 874篇 |
2007年 | 918篇 |
2006年 | 808篇 |
2005年 | 853篇 |
2004年 | 853篇 |
2003年 | 804篇 |
2002年 | 747篇 |
2001年 | 143篇 |
2000年 | 134篇 |
1999年 | 201篇 |
1998年 | 191篇 |
1997年 | 132篇 |
1996年 | 129篇 |
1995年 | 111篇 |
1994年 | 106篇 |
1993年 | 108篇 |
1992年 | 115篇 |
1991年 | 85篇 |
1990年 | 87篇 |
1989年 | 92篇 |
1988年 | 66篇 |
1987年 | 77篇 |
1986年 | 62篇 |
1985年 | 69篇 |
1984年 | 69篇 |
1983年 | 55篇 |
1982年 | 78篇 |
1981年 | 55篇 |
1980年 | 62篇 |
1979年 | 45篇 |
1978年 | 40篇 |
1977年 | 36篇 |
1976年 | 39篇 |
1975年 | 40篇 |
1974年 | 21篇 |
1973年 | 29篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
Changes in Electrophoretic Patterns of Oocyte Proteins during Oocyte Maturation in Oryzias latipes 总被引:2,自引:2,他引:0
Takashi Iwamatsu Susumu Y. Takahashi Masamichi Oh-ishi Takashi Yokochi Hiroko Maeda 《Development, growth & differentiation》1992,34(2):173-179
Changes in the two-dimensional SDS-electrophoretic patterns of extracts of maturing denuded oocytes of the medaka ( Oryzias latipes ) were surveyed. In oocytes without follicular constituents several proteins became detectable in the area between the acidic and slightly basic proteins on the two-dimensional electrophoretograms, while a few of the protein spots disappeared during the process of oocyte maturation. The former proteins were detected also in oocytes that were induced to mature in vivo without breakdown of the germinal vesicle. Several proteins newly observed in extracts of post-vitellogenic oocytes during maturation after breakdown of the germinal vesicle were also identified by two-dimensional electrophoresis. Of several proteins that exhibited noticeable changes in maturing oocytes, only one spot incorporated 14 C-labeled amino acid during maturation, suggesting that post-translational modification of many proteins occurred during oocyte maturation. 相似文献
102.
103.
Changes in activities of enzymes and levels of antioxidant substratesinvolved in the -detoxification system in seedlings of rice (Oryza sativa L. cv. Yamabiko) inresponse to variations in the oxygen environment were studied.Activities of superoxide dismutase, ascorbate peroxidase, monodehydroascorbatereductase, dehydroascorbate reductase, glutathione reductaseand catalase, expressed either on the basis of fresh weightof shoots or relative to levels of soluble protein were muchlower in seedlings germinated under water for 6 days than inthose germinated in air for the same period of time. When submergedseedlings were exposed to air, the activities of these six enzymesincreased to or exceeded the levels in aerobically grown controlsduring 24 h of adaptation to air. Ascorbate and glutathione,which act as antioxidant substrates in the -detoxification system, were present in submergedseedlings at nearly the same levels as those found in aerobicallygrown controls. On exposure of submerged seedlings to air, thelevel of ascorbate in creased slightly, but the level of glutathioneshowed a rapid increase, reaching 7 times that in aerobicallygrown controls within 12 h of adaptation to air. Levels of allsix antioxidative enzymes and of two substrates involved inthe detoxification of the superoxide radical increased withincreases in oxygen tension in the environment. Moreover, thedevelopment of this system consisted of two steps, namely, arapid increase in the level of glutathione and a subsequentslow increase in the activities of antioxidative enzymes.
1 Present address: Research Institute for Bioresources, OkayamaUniversity, Kurashiki, 710 Japan. 相似文献
104.
T Shimada E Hamada A Terano T Sugimoto Y Kurachi 《Biochemical and biophysical research communications》1991,179(1):327-332
ACh causes a long-lasting inhibition of STOCs via G proteins in intestinal smooth muscle cells. We examined the effects of isoproterenol (Iso) on the ACh-induced inhibition of STOCs in isolated ileal smooth muscle cells using the G omega-seal whole cell clamp technique. In control, ACh (1 microM) completely suppressed STOCs, which did not desensitize over a period lasting 20 minutes. When Iso (10 microM) was added to the bath in the presence of ACh, the ACh-induced inhibition of STOCs was gradually removed. This effect of Iso was prevented by propranolol (10 microM). Application of Db-cAMP (500 microM) mimicked the Iso effects. Intracellulary applied GTP-gamma S (100 microM) gradually suppressed STOCs in the absence of ACh, which could not be removed by either Iso or Db-cAMP. These results suggest that beta-adrenergic stimulation causes a removal of the muscarinic inhibition of STOCs via a cAMP-dependent process. 相似文献
105.
To study the distribution of rhodanese (E.C. 2.8.1.1) in plants, rhodanese activity was assayed on 13 cyanogenic and 12 non-cyanogenic
species. All the species tested had the enzyme activity. This phenomenon leads to a hypothesis that the enzyme is generally
distributed in plants. 相似文献
106.
Takashi Ariizumi Naomi Moriya Hideho Uchiyama Makoto Asashima 《Development genes and evolution》1991,200(4):230-233
Summary Human recombinant activin A, which is identical with erythroid differentiation factor (EDF), was tested for its mesoderm-inducing activity in concentrations from 0.3–50 ng/ml, using ectoderm of Xenopus late blastula (Stage 9) as the responding tissue. At a low concentration of activin A, blood-like cells, mesenchyme, and coelomic epithelium were induced; at a moderate concentration muscle and neural tissue, and at a high concentration notochord. Activin A thus induced all mesodermal tissues in a dose-dependent manner, such that a low dose induced ventral structures and a high dose induced dorsal structures. Activin may act as an intrinsic inducing molecule responsible for establishing the dorso-ventral axis in early Xenopus development.
Offprint requests to: M. Asashima 相似文献
107.
108.
109.
Kiyoshi Ohkawa Takashi Hatano Naoko Takizawa Kazue Shinmoto Kyosuke Yamada Makoto Matsuda Koji Takada Yutaka Tsukada 《In vitro cellular & developmental biology. Animal》1992,28(6):449-454
Summary A human yolk sac tumor cell line, TG1, which was established from a testicular yolk sac tumor, was found to replicate continuously
in a chemically defined medium supplemented with Na2SeO3 (ISRPMI). TG1 produced several plasma proteins and growth factors: albumin, alpha-fetoprotein (AFP), ferritin, carcinoembryonic
antigen, beta-2-microglobulin, polyamine, neuron specific enolase, tissue polypeptide antigen, transferrin (Tf), epidermal
growth factor, and platelet derived growth factor. By analysis of lectin (LcHA)-affinity electrophoresis, to examine the microheterogeneity
of carbohydrate chains of synthetic glycoproteins, TG1 cells cultured with ISRPMI produced only LcHA reactive Tf and AFP based
on core fucose attached to asparagine-linkedN-acetylglucosamine residues instead of LcHA-nonreactive Tf and AFP produced by TG1 cells cultured with fetal bovine serum
(FBS)-containing medium.α1-6 Fucosyltransferase activity was significantly greater in the TG1 cells cultured with ISRPMI (39.9±1.5 pmol · h−1 · mg−1 protein) than cultured with FBS-containing media (18.2±1.2 pmol · h−1 · mg−1 protein). These results have indicated that the selective increase ofα1-6 fucosyltransferase occurred when the cells were cultured with the FBS-free synthetic media. 相似文献
110.