全文获取类型
收费全文 | 87063篇 |
免费 | 6398篇 |
国内免费 | 5087篇 |
出版年
2024年 | 111篇 |
2023年 | 956篇 |
2022年 | 2585篇 |
2021年 | 4366篇 |
2020年 | 2841篇 |
2019年 | 3504篇 |
2018年 | 3504篇 |
2017年 | 2567篇 |
2016年 | 3630篇 |
2015年 | 5406篇 |
2014年 | 6253篇 |
2013年 | 6746篇 |
2012年 | 8003篇 |
2011年 | 7097篇 |
2010年 | 4312篇 |
2009年 | 3829篇 |
2008年 | 4414篇 |
2007年 | 3968篇 |
2006年 | 3413篇 |
2005年 | 2852篇 |
2004年 | 2445篇 |
2003年 | 2037篇 |
2002年 | 1699篇 |
2001年 | 1482篇 |
2000年 | 1424篇 |
1999年 | 1325篇 |
1998年 | 756篇 |
1997年 | 714篇 |
1996年 | 715篇 |
1995年 | 672篇 |
1994年 | 600篇 |
1993年 | 415篇 |
1992年 | 648篇 |
1991年 | 510篇 |
1990年 | 461篇 |
1989年 | 329篇 |
1988年 | 279篇 |
1987年 | 256篇 |
1986年 | 193篇 |
1985年 | 217篇 |
1984年 | 121篇 |
1983年 | 131篇 |
1982年 | 84篇 |
1981年 | 69篇 |
1980年 | 57篇 |
1979年 | 80篇 |
1977年 | 48篇 |
1974年 | 54篇 |
1973年 | 42篇 |
1972年 | 39篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
Antigenic proteins of 36 and 29 kDa were localized in Spirometra mansoni plerocercoid (sparganum) immunohistochemically by avidin biotin complex (ABC) staining. When polyclonal antibodies such as BALB/c mouse serum immunized with crude saline extract of sparganum or confirmed sparganosis sera were reacted as primary antibodies, the positive chromogen (3-amino, 9-ethylcarbazole) reactions were recognized at syncytial tegument, tegumental cells, muscle and parenchymal cells and lining cells of excretory canals. A monoclonal antibody (MAb) which was reacting to 36 and 29 kDa proteins in the extract of the worm was localized at the syncytial tegument and tegumental cells. The present results suggested that the potent antigenic proteins of 36 and 29 kDa in sparganum were produced at the tegumental cells and transported to the syncytial tegument. 相似文献
992.
C Sato J H Liu L Tang Y Sakai T Yauchi N Izumi J Liu T Takano F Marumo 《Life sciences》1992,51(26):2057-2063
We investigated the effects of protein kinase C modulations and calcium mobilization on GSH efflux in Hep G2 cells. GSH efflux from Hep G2 cells was increased by a phorbol ester. Staurosporine, an inhibitor of protein kinase C, diminished phorbol ester-stimulated GSH efflux from the cells. GSH efflux was negatively correlated with extracellular calcium concentrations. Verapamil enhanced GSH efflux, whereas ATP decreased GSH efflux. The latter effect was diminished in the absence of extracellular calcium. Protein kinase C and calcium mobilization may be crucial factors in GSH efflux from human hepatocytes. 相似文献
993.
Previous studies on osteoarthritic changes induced by intraarticular injections of estradiol benzoate (EB) suggest estrogen as a risk factor in the development of knee osteoarthritis (OA). The present study observed the anti-arthritic effects of tamoxifen (TMX). Oophorectomized rabbits were subjected to intraarticular injections of vehicle control, EB, TMX, or EB/TMX for 3 weeks. The cartilage changes were assessed by light and scanning electron microscopic examination, enzyme histochemical analysis, and the amount of alcian blue stain binding to glycosaminoglycans. EB injections resulted in cell necrosis, chondrocyte clonings, and pittings, whereas the vehicle control, TMX, and EB/TMX-injected groups showed no histologic abnormalities. Histochemical analysis showed that the numbers of lactate dehydrogenase (LDH)-reactive chondrocytes in the EB-injected group were significantly reduced when compared to other groups (p less than 0.001). The injections of EB/TMX significantly reduced the chondrocyte numbers in the lateral superficial layer (p less than 0.05), compared with the vehicle injection. TMX-injected group revealed slight although insignificant decreases in chondrocyte numbers. The amount of alcian blue stains, representing the relative amount of proteoglycans, significantly decreased only in the superficial layer of the EB- and EB/TMX-injected groups (p less than 0.05). TMX, when concurrently injected with EB, antagonized the chondrodestructive effects of estradiol at the early stage of knee OA in rabbits. The results suggest the potential therapeutic use of TMX at the early stage of OA. 相似文献
994.
The circadian rhythm of 6-sulphatoxymelatonin (aMT6s) excretion has been determined in male and female rats at 3 weeks and at 2, 8, 14 and 20 months of age. All animals have a pronounced circadian pattern of aMT6s excretion under a 12 hour dark: 12 hour light cycle. A significant increase in aMT6s excretion is observed from 3 weeks to 14 months followed by a decrease at 20 months. There is a highly significant correlation between aMT6s excretion and body weight (r = 0.73 for female rats and r = 0.74 for male rats; p values are all less than 0.001). Thus, a decrease in aMT6s excretion associated with increasing age occurs when body weight is taken into consideration. aMT6s excretion is higher in males at 3 weeks and at 2 and 8 months of ages. Urinary testosterone in male rats and estradiol in female rats increase from 3 weeks to 8 months and decrease at older ages. These data suggest that increase of body weight from 3 weeks to 14 months is an important factor responsible for the age-related alteration. The sex differences in aMT6s excretion in younger rats may be associated with their sex hormonal milieu. 相似文献
995.
996.
Pollen is an excellent source of actin for biochemical and physiological studies of the actomyosin system in higher plants. We have developed an efficient method to prepare relatively high levels of actin from the pollen of maize (Zea mays L.). The procedures of purification include acetone powder preparation, saturated ammonium sulfate fractionation, diethylaminoethyl-cellulose chromatography, a cycle of polymerization-depolymerization, and Sephacryl S-200 gel filtration. The average yield of actin is 19 milligrams per 100 grams of pollen grains extracted. This is comparable with those of Acanthamoeba castellanii and human platelets. The purified pollen actin is electrophoretically homogeneous and its molecular mass is 42 kilodaltons. The amino acid composition and circular dichroism spectrum of pollen actin are identical to those of muscle actin. The actin purified from pollen is able to polymerize to F-actin. The pollen F-actin activated the activity of the muscle myosin ATPase sevenfold. 相似文献
997.
Two new compounds, pedicularioside E and F, were isolated from whole plants of Pedicularis lasiophrys, along with the four known compounds, verbascoside, cistanoside C, cistanoside D and 8-epiloganin. On the basis of spectral and chemical evidence, pedicularioside E and F were identified to be 1'-O-beta-D-(3-methoxy-4-hydroxy-beta-phenyl)-ethyl-6'-O-feruloyl- alpha-L-(2-acetyl)-rhamnosyl-(1----3')-4'-acetylglucopyranoside and shanzhisin methyl ester cellobioside, respectively. 相似文献
998.
Triterpenoid saponins from Clinopodium polycephalum. 总被引:4,自引:0,他引:4
A new triterpenoid saponin, clinopodiside A, has been isolated from Clinopodium polycephalum. Its structure was established by spectroscopic methods and X-ray diffraction analysis as 3-O-beta-D-glucopyranosyl(1----6)-[ beta-D-glucopyranosyl (1----4)]-beta-D-glucopyranosyl-olean-11,13(18)-diene-3 beta,16 beta, 23,28-tetrol. 相似文献
999.
Diversity and origins of endophytic fungal symbionts of the North American grass Festuca arizonica 总被引:3,自引:0,他引:3
Z.-q. An J.-S. Liu M. R. Siegel G. Bunge C. L. Schardl 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》1992,85(2-3):366-371
Summary
Acremonium spp. endophytes are mutualistic fungal symbionts of many C3 grasses. They are anamorphs of Epichloë typhina (Clavicipitaceae) that have become strictly seedborne, heritable components of symbiotic units (symbiota). In order to test the possibility that endophytes may contribute to the genetic diversity of symbiota, a survey was conducted of plants from nine populations of Festuca arizonica in the southern Rocky Mountains. Sequence analysis of rRNA gene segments distinguished three Acremonium endophyte types. Parsimony analysis indicated at least two distinct evolutionary origins of the Acremonium endophytes from E. typhina. Either or both of these evolutionary lineages may have involved cospeciation with the host. 相似文献
1000.
Y Liu D Peter A Roghani S Schuldiner G G Privé D Eisenberg N Brecha R H Edwards 《Cell》1992,70(4):539-551