全文获取类型
收费全文 | 318682篇 |
免费 | 37306篇 |
国内免费 | 137篇 |
专业分类
356125篇 |
出版年
2018年 | 2748篇 |
2016年 | 3742篇 |
2015年 | 5067篇 |
2014年 | 5995篇 |
2013年 | 8631篇 |
2012年 | 9575篇 |
2011年 | 9747篇 |
2010年 | 6597篇 |
2009年 | 5892篇 |
2008年 | 8535篇 |
2007年 | 8964篇 |
2006年 | 8371篇 |
2005年 | 8079篇 |
2004年 | 8165篇 |
2003年 | 7902篇 |
2002年 | 7801篇 |
2001年 | 14293篇 |
2000年 | 14321篇 |
1999年 | 11475篇 |
1998年 | 4020篇 |
1997年 | 4129篇 |
1996年 | 3928篇 |
1995年 | 3799篇 |
1994年 | 3800篇 |
1993年 | 3689篇 |
1992年 | 9805篇 |
1991年 | 9386篇 |
1990年 | 9211篇 |
1989年 | 8940篇 |
1988年 | 8347篇 |
1987年 | 7985篇 |
1986年 | 7211篇 |
1985年 | 7319篇 |
1984年 | 6043篇 |
1983年 | 5301篇 |
1982年 | 4173篇 |
1981年 | 3691篇 |
1980年 | 3511篇 |
1979年 | 6094篇 |
1978年 | 4547篇 |
1977年 | 4272篇 |
1976年 | 3968篇 |
1975年 | 4295篇 |
1974年 | 4651篇 |
1973年 | 4715篇 |
1972年 | 4355篇 |
1971年 | 4065篇 |
1970年 | 3435篇 |
1969年 | 3334篇 |
1968年 | 2962篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
The fine structure of meiotic chromosome pairing in natural and artificial Lilium polyploids 总被引:1,自引:0,他引:1
P B Moens 《Journal of cell science》1970,7(1):55-63
92.
93.
Six hundred foramina transversaria (FT) of the axis vertebrae of 4 population groups were examined for the presence of erosion of the lateral articular mass. Of these, 127 (21%) and 72 (12%) presented with moderate and marked erosion, respectively. Evidence is presented incriminating the tortuosity of the vertebral artery as well as congenital factors in the etiology of the erosion of the FT. Attention is drawn to the possible correlation between angulation of the transverse process of the axis and erosion of the FT. 相似文献
94.
Two internal herinias of the intestines were found in adult males. One was a large translucent avascular membranous sac contining the small intestine from the duodenojejunal flexure to a point 6 in. proximal to the ileocaecal junction. The other was a peritoneal sac enclosing the small intestine, appendix, caecum and 6 in. of the ascending colon. The mesenteric and colic vessels were normal. Both hernias conformed to PAPEZ's concept of the so-called paraduodenal hernia that the hernial sac is derived from the umbilical coelom. The authors suggest that most of the so-called paraduodenal hernias are derived from the embryonic umbilical peritoneal diverticulum rather than from the peritoneal recesses or mesentery of the colon. 相似文献
95.
96.
The liver and kidney of rat underwent severe histopathological lesions when treated with a single bolus dose of carbendazim, a fungicide, particularly affecting the hepatocytes and the renal corpuscles, respectively. The effects appear to be manifestations of the microtubule-disrupting activity of carbendazim. Treatment of carbendazim-treated rats with the powder of tuberous root of Withania somnifera (Ashwagandha) for 48 days resulted in complete cure of these organs. The results indicate that Withania somnifera would be an effective curative for carbendazim-induced histopathological changes in the liver and kidney. 相似文献
97.
Bertin N.; Guichard S.; Leonardi C.; Longuenesse J. J.; Langlois D.; Navez B. 《Annals of botany》2000,85(6):741-750
Changes in yield and quality of fresh tomatoes in response toair vapour pressure deficit (VPD) and plant fruit load werestudied under Mediterranean summer conditions. Plants thinnedto three or six fruits per truss were grown in two compartments,one at a VPD below 1.5 kPa, the other without VPD control. Theseasonal trend in fruit yield and quality was assessed fromApril to September by weekly measurement of number, fresh weightand dry matter content of harvested fruits, together with theoccurrence of blossom-end-rot (BER) and cracking. On two occasions,in July and September, sugar and acid content was measured atthree ripening stages. The seasonal decrease in fresh yieldwas attenuated at low VPD, because of higher individual fruitfresh weight, especially at low fruit load. Low VPD decreasedoccurrence of BER but like low fruit load, it increased fruitcracking. Fruit dry matter content was lower at low VPD, butwas unaffected by fruit load. Sugar content and the ratio ofsugars:acids was increased at high VPD and low fruit load, withinteractive effects depending on season and ripening stage.The influence of VPD on acid content differed with fruit loadand also changed during ripening and between seasons. Resultsshowed that water was the main limiting factor for growth offruits picked in July; at this time, reducing fruit load topromote mean fruit size had negative effects on BER and cracking.Reducing VPD reduced BER but had a negative effect on crackingand diluted both the dry matter and sugar content. For fruitsharvested later in summer, these negative effects were attenuatedbecause fruit growth was also carbon limited. Copyright 2000Annals of Botany Company Lycopersicon esculentum Mill., tomato, water and carbon stress, yield, quality, dry matter, sugar, acid, BER, volatile composition 相似文献
98.
Cyanobacteria are prominent constituents of the marine biosphere that account for a significant percentage of oceanic primary productivity. In an effort to resolve how open-ocean cyanobacteria persist in regions where the Fe concentration is thought to be limiting their productivity, we performed a number of Fe stress experiments on axenic cultures of marine Synechococcus spp., Crocosphaera sp., and Trichodesmium sp. Through this work, we determined that all of these marine cyanobacteria mount adaptive responses to Fe stress, which resulted in the induction and/or repression of several proteins. We have identified one of the Fe stress-induced proteins as an IdiA homologue. Genomic observations and laboratory data presented herein from open-ocean Synechococcus spp. are consistent with IdiA having a role in cellular Fe scavenging. Our data indicate that IdiA may make an excellent marker for Fe stress in open-ocean cyanobacterial field populations. By determining how these microorganisms respond to Fe stress, we will gain insight into how and when this important trace element can limit their growth in situ. This knowledge will greatly increase our understanding of how marine Fe cycling impacts oceanic processes, such as carbon and nitrogen fixation. 相似文献
99.
K. H. Jang J. W. Seo K. B. Song C. H. Kim S. K. Rhee 《Bioprocess and biosystems engineering》1999,21(5):453-458
Secretion of levansucrase from Zymomonas mobilis in Escherichiacoli by glycine supplement was investigated. A significant amount of levansucrase (about 25% of total activity) was found in intact whole-cells. Cell fractionation experiments showed that levansucrase was found both in the periplasmic space and in the cytoplasmic fraction of E. coli. None or only trace amounts of levansucrase was detected in the extracellular culture broth at 24 h of cultivation and it accrued with the increasing concentration of glycine in the culture medium and duration of the culture period. Optimal glycine concentration for the maximum secretion of levansucrase was in the range of 0.8-1%, in which approximately 20-50% of levansucrase was released into the extracellular fraction at 24 h of cultivation, although glycine retarded the bacterial growth. 相似文献