全文获取类型
收费全文 | 778693篇 |
免费 | 88376篇 |
国内免费 | 898篇 |
专业分类
867967篇 |
出版年
2018年 | 7052篇 |
2017年 | 6941篇 |
2016年 | 9646篇 |
2015年 | 13569篇 |
2014年 | 15687篇 |
2013年 | 22134篇 |
2012年 | 25562篇 |
2011年 | 26033篇 |
2010年 | 17356篇 |
2009年 | 16004篇 |
2008年 | 23216篇 |
2007年 | 23677篇 |
2006年 | 22432篇 |
2005年 | 21359篇 |
2004年 | 21269篇 |
2003年 | 20191篇 |
2002年 | 19631篇 |
2001年 | 33118篇 |
2000年 | 33270篇 |
1999年 | 26864篇 |
1998年 | 10025篇 |
1997年 | 10175篇 |
1996年 | 9808篇 |
1995年 | 9117篇 |
1994年 | 9016篇 |
1993年 | 8914篇 |
1992年 | 22578篇 |
1991年 | 22128篇 |
1990年 | 21754篇 |
1989年 | 21339篇 |
1988年 | 19650篇 |
1987年 | 18647篇 |
1986年 | 17573篇 |
1985年 | 17508篇 |
1984年 | 14364篇 |
1983年 | 12519篇 |
1982年 | 9549篇 |
1981年 | 8565篇 |
1980年 | 8122篇 |
1979年 | 13725篇 |
1978年 | 10876篇 |
1977年 | 9769篇 |
1976年 | 9313篇 |
1975年 | 10392篇 |
1974年 | 11118篇 |
1973年 | 10923篇 |
1972年 | 9839篇 |
1971年 | 8917篇 |
1970年 | 7687篇 |
1969年 | 7362篇 |
排序方式: 共有10000条查询结果,搜索用时 7 毫秒
991.
992.
Gender identification of shovelnose sturgeon using ultrasonic and endoscopic imagery and the application of the method to the pallid sturgeon 总被引:7,自引:0,他引:7
M. L. Wildhaber† D. M. Papoulias† A. J. DeLonay† D. E. Tillitt† J. L. Bryan† M. L. Annis† J. A. Allert† 《Journal of fish biology》2005,67(1):114-132
Monthly sampling of shovelnose sturgeon Scaphirhynchus platorynchus , a biological surrogate for the endangered pallid sturgeon Scaphirhynchus albus , was conducted to develop a multi‐seasonal profile of reproductive stages. Data collected included histological characteristics of gonads from wild caught fish and laboratory and field ultrasonic and endoscopic images. These data were used to compare effectiveness of ultrasonic and endoscopic techniques at identifying gender of adult shovelnose sturgeon at different reproductive stages. The least invasive method ( i.e . ultrasound) was least effective while the most invasive ( i.e . endoscope through an abdominal incision) was the most effective at identifying shovelnose sturgeon gender. In most cases, success rate for identifying males was greater than females, with success at identifying both genders greater in more advanced reproductive stages. Concomitantly, for most months average reproductive stage was more advanced for males than females. April and May were the months with the most advanced reproductive stage, and were the months when ultrasound was most effective. Methods were also applied in the Upper Missouri River to validate their use on pallid sturgeon Scaphirhynchus albus . Ultrasound was successful at identifying pallid sturgeon gender, however, endoscopic examination through the urogenital duct was only successful at identifying pallid sturgeon gender when the urogenital duct was not opaque. 相似文献
993.
Martin L. Adamson 《Systematic parasitology》1981,3(4):209-216
Summary
Rhigonema infecta (Leidy, 1849) Christie & Cobb, 1927, a member of the family Rhigonematidae sensu Théodoridès, 1965, is redescribed from the diplopod Narceus annularis from Sharbot Lake and Long Point, Ontario, Canada. R. infecta is most similar to R. subtruncatum Dollfus, 1952 but differs from this species in possessing four rather than three post-cloacal papillae in the male. Rhigonematids have been affiliated with members of the order Oxyurida by most authors but study of R. infecta suggests that rhigonematids should be placed in their own order, the Rhigonematida. Members of the order Rhigonematida are characterized by: two spicules in the male; H-shaped excretory system; are round to oval sperms; thick and smooth egg-shell; apparently lacking a uterine layer; and development in the egg involving no moults and resulting in a long, thin, coiled larva. In contrast, oxyuridans have a single spicule, the excretory system is X-shaped, the sperm is comet-shaped and the egg-shell has a prominent striated uterine layer. Development in the egg involves at least one and probably two moults and results in a short, robust, uncoiled larva. ac]19810310 相似文献
994.
995.
996.
Brigitta M. N. Brinkman Eric L. Kaijzel Tom W. J. Huizinga Marius J. Giphart Ferdinand C. Breedveld Cornelis L. Verweij 《Human genetics》1995,96(4):493-493
We have identified a C-insertion polymorphism in the 5'UTR of the first exon of the human tumor necrosis factor alpha (TNFA) gene. TNFA is a cytokine that plays an important role in the inflammatory response. 相似文献
997.
The RAD6 gene of Saccharomyces cerevisiae, which encodes a ubiquitin-conjugating enzyme, is required for DNA repair, DNA damage-induced mutagenesis and sporulation. To evaluate the biological relevance of the thioester adduct between RAD6 protein and ubiquitin, formed as an obligatory, transient intermediate during ubiquitin conjugation to substrates, we altered cysteine 88 in RAD6 to serine. Esterification with ubiquitin occurs at serine 88 in the mutant protein, but conjugation of ubiquitin to the test substrate histone H2A is inactivated. Phenotypically, strains harboring the rad6 Ser88 allele are indistinguishable from rad6 deletion (rad6 delta) mutant cells. These findings argue against ligation of ubiquitin at cysteine 88 acting as a functional switch of a cryptic biochemical activity in RAD6. 相似文献
998.
Serum proteins [molecular weight (MW) > 10,000] are essential for increased insulin-stimulated glucose transport after in vitro muscle contractions. We investigated the role of the kallikrein-kininogen system, including bradykinin, which is derived from kallikrein (MW > 10,000)-catalyzed degradation of serum protein kininogen (MW > 10,000), on this contraction effect. In vitro electrical stimulation of rat epitrochlearis muscles was performed in 1) rat serum +/- kallikrein inhibitors; 2) human plasma (normal or kallikrein-deficient); 3) rat serum +/- bradykinin receptor-2 inhibitors; or 4) serum-free buffer +/- bradykinin. 3-O-methylglucose transport (3-MGT) was measured 3.5 h later. Serum +/- kallikrein inhibitors tended (P = 0.08) to diminish postcontraction insulin-stimulated 3-MGT. Contractions in normal plasma enhanced insulin-stimulated 3-MGT vs. controls, but contractions in kallikrein-deficient plasma did not. Supplementing rat serum with bradykinin receptor antagonist HOE-140 during contraction did not alter insulin-stimulated 3-MGT. Muscles stimulated to contract in serum-free buffer plus bradykinin did not have enhanced insulin-stimulated 3-MGT. Bradykinin was insufficient for postcontraction-enhanced insulin sensitivity. However, results with kallikrein inhibitors and kallikrein-deficient plasma suggest kallikrein plays a role in this improved insulin action. 相似文献
999.
1000.