全文获取类型
收费全文 | 100803篇 |
免费 | 898篇 |
国内免费 | 897篇 |
专业分类
102598篇 |
出版年
2022年 | 69篇 |
2021年 | 112篇 |
2020年 | 60篇 |
2019年 | 84篇 |
2018年 | 11905篇 |
2017年 | 10744篇 |
2016年 | 7648篇 |
2015年 | 890篇 |
2014年 | 623篇 |
2013年 | 723篇 |
2012年 | 4696篇 |
2011年 | 13274篇 |
2010年 | 12304篇 |
2009年 | 8479篇 |
2008年 | 10171篇 |
2007年 | 11713篇 |
2006年 | 633篇 |
2005年 | 862篇 |
2004年 | 1266篇 |
2003年 | 1365篇 |
2002年 | 1094篇 |
2001年 | 357篇 |
2000年 | 258篇 |
1999年 | 113篇 |
1998年 | 82篇 |
1997年 | 95篇 |
1996年 | 65篇 |
1995年 | 53篇 |
1994年 | 74篇 |
1993年 | 90篇 |
1992年 | 111篇 |
1991年 | 110篇 |
1990年 | 74篇 |
1989年 | 82篇 |
1988年 | 77篇 |
1987年 | 69篇 |
1985年 | 52篇 |
1984年 | 84篇 |
1983年 | 77篇 |
1982年 | 64篇 |
1981年 | 67篇 |
1980年 | 68篇 |
1979年 | 49篇 |
1978年 | 70篇 |
1977年 | 59篇 |
1976年 | 54篇 |
1975年 | 49篇 |
1973年 | 51篇 |
1972年 | 288篇 |
1971年 | 301篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
J M Gallo D Escalier P Grellier E Précigout M Albert G David J Schrével 《The journal of histochemistry and cytochemistry》1991,39(3):273-282
Among the monoclonal antibodies (MAb) selected after immunization of mice with a detergent-insoluble fraction from human spermatozoa, MAb 4D4 was found to stain in immunofluorescence the principal part of the acrosome of human spermatozoa. Acrosome reaction induced decreased and spotty 4D4 immunofluorescence staining. Immunoelectron microscopy before or after embedding revealed that the epitope defined by MAb 4D4 was sequestered in the anterior acrosomal matrix and, after the acrosome reaction, remained partly bound on matrix elements attached to the inner acrosomal membrane. Western blot analysis of sperm extracts showed that the epitope defined by MAb 4D4 was located on a 55 KD polypeptide in whole cells and on 55 and 50 KD polypeptides in non-ionic detergent fractions. Human proacrosin-enriched fraction obtained by FPLC purification exhibited several proteolytic activities against gelatin in gel enzymography: a 50 KD major band and two minor bands in the 20-30 KD area; the 50 KD polypeptide reacted with MAb 4D4 in Western blots. Furthermore, the 4D4-immunoprecipitated polypeptide from sperm extract showed that the 50 KD band exhibited proteolytic activity with an optimal pH at 8.0 that was strongly inhibited by soybean trypsin inhibitor and ZnCl2. MAb 4D4 also reacted with the acrosome of the monkey Macaca fascicularis but not with the acrosome of any of the other non-primate mammalian species examined so far. Various shape defects of the acrosomal principal region were revealed by 4D4 labeling of spermatozoa with head anomalies from infertile patients. MAb 4D4 also recognized proacrosin in paraffin-embedded human testis sections. These data make the monoclonal antiproacrosin antibody 4D4 an efficient tool for evaluation of the acrosomal status of human spermatozoa and spermatids. 相似文献
102.
Takahiro Ishii Tatsufumi Okino Yosuke Mino Hiroaki Tamiya Fuyuhiko Matsuda 《Plant Growth Regulation》2007,52(2):131-139
Starfish waste has been shown to be an effective compost material not only in the promotion of plant growth but also in terms
of having insecticidal activity. In the present study, plant growth regulation by chemicals from starfish was examined. The
aqueous fraction from a hot water extract of the starfish Asterias amurensis Lütken showed plant-growth activity, while the aqueous fraction from a methanol extract inhibited growth of Brassica campestris. The lipophilic fraction from the methanol extract also exhibited a plant growth-promoting effect. The active components
from each extract were identified. Asterubine from the hot water extract promoted plant growth. A ceramide from the lipophilic
fraction showed root growth promoting effect, and three glucocerebrosides had promotive effects on the entire plant. Asterosaponins
were identified as the main growth inhibitors in the aqueous fraction of the methanol extract. These active compounds from
starfish waste could be analyzed as potential plant growth regulators in agricultural applications in the future. 相似文献
103.
This editorial addresses the debate concerning the origin of adult nucleus pulposus cells in the light of profiling studies
by Minogue and colleagues. In their report of several marker genes that distinguish nucleus pulposus cells from other related
cell types, the authors provide novel insights into the notochordal nature of the former. Together with recently published
work, their work lends support to the view that all cells present within the nucleus pulposus are derived from the notochord.
Hence, the choice of an animal model for disc research should be based on considerations other than the cell loss and replacement
by non-notochordal cells. 相似文献
104.
105.
Kevin B. Potts 《Journal of Mammalian Evolution》2010,17(3):221-222
106.
107.
108.
Background
Arsenic contamination is widespread throughout the world and this toxic metalloid is known to cause cancers of organs such as liver, kidney, skin, and lung in human. In spite of a recent surge in arsenic related studies, we are still far from a comprehensive understanding of arsenic uptake, detoxification, and sequestration in plants. Crambe abyssinica, commonly known as 'abyssinian mustard', is a non-food, high biomass oil seed crop that is naturally tolerant to heavy metals. Moreover, it accumulates significantly higher levels of arsenic as compared to other species of the Brassicaceae family. Thus, C. abyssinica has great potential to be utilized as an ideal inedible crop for phytoremediation of heavy metals and metalloids. However, the mechanism of arsenic metabolism in higher plants, including C. abyssinica, remains elusive. 相似文献109.
Albert R. K.; Lamm W. J.; Henderson W. R.; Bolin R. W. 《Journal of applied physiology》1989,66(1):458-464
Leukotrienes (LTs) C4 and D4 are vasoconstrictors and are thought to increase both systemic and pulmonary vascular permeability. However, we and others have observed that LTC4 and LTD4 cause pulmonary vasoconstriction but do not increase the fluid filtration coefficient of excised guinea pig lungs perfused with a cell-depleted perfusate. To determine what vascular segments were exposed to an LT-induced increase in intravascular hydrostatic pressure we measured pulmonary arterial (Ppa), pulmonary arterial occlusion (Po,a), venous (Po,v) and double occlusion (Pdo) pressures in isolated guinea pig lungs perfused with a cell-depleted buffered salt solution before and after injecting 4 micrograms of LTB4, LTC4, or LTD4 into the pulmonary artery. All three LTs increased airway pressures and also increased Ppa, Po,a, and Pdo. Histamine (15 micrograms) as well as serotonin (20 or 200 micrograms) had the same effect. In excised rabbit lungs, histamine and serotonin increased only Ppa, and Po,a. LTC4 had no vasoactivity. There are marked species variations with regard to the activity and site of action of histamine, serotonin, and LTC4 on the pulmonary circulation. 相似文献
110.