全文获取类型
收费全文 | 1147篇 |
免费 | 102篇 |
国内免费 | 3篇 |
出版年
2021年 | 17篇 |
2020年 | 9篇 |
2017年 | 13篇 |
2016年 | 21篇 |
2015年 | 46篇 |
2014年 | 51篇 |
2013年 | 57篇 |
2012年 | 77篇 |
2011年 | 81篇 |
2010年 | 45篇 |
2009年 | 29篇 |
2008年 | 54篇 |
2007年 | 61篇 |
2006年 | 51篇 |
2005年 | 47篇 |
2004年 | 52篇 |
2003年 | 47篇 |
2002年 | 46篇 |
2001年 | 10篇 |
1999年 | 14篇 |
1998年 | 18篇 |
1997年 | 7篇 |
1996年 | 11篇 |
1995年 | 7篇 |
1994年 | 15篇 |
1993年 | 16篇 |
1991年 | 12篇 |
1990年 | 15篇 |
1989年 | 16篇 |
1988年 | 6篇 |
1987年 | 7篇 |
1986年 | 6篇 |
1985年 | 9篇 |
1984年 | 12篇 |
1983年 | 8篇 |
1981年 | 10篇 |
1980年 | 18篇 |
1978年 | 10篇 |
1977年 | 13篇 |
1976年 | 9篇 |
1975年 | 12篇 |
1973年 | 19篇 |
1972年 | 9篇 |
1971年 | 8篇 |
1969年 | 13篇 |
1968年 | 10篇 |
1967年 | 8篇 |
1966年 | 6篇 |
1965年 | 7篇 |
1964年 | 9篇 |
排序方式: 共有1252条查询结果,搜索用时 109 毫秒
81.
82.
83.
Our objective was to determine the feasibility of prompt reinsemination of dairy cows when diagnosed not pregnant 27-29 days after first-service timed AI (TAI). We assumed that a first-wave dominant follicle was present at that time that would ovulate in response to GnRH once precocious luteal regression was induced after administration of PGF(2alpha). Cows that had not been detected in estrus and reinseminated by Days 27-29 after a first-service TAI were diagnosed not pregnant by ultrasonography. Nonpregnant cows from three herds were assigned randomly to receive either no further treatment until reinsemination (controls; n=189); 25mg i.m. of PGF(2alpha) and then reinsemination according to detected estrus (81 of 108) or at 72-80h after PGF(2alpha) treatment (PGF) in the absence of estrus (27 of 108); or 25mg i.m. of PGF(2alpha) followed by 100 microg i.m. of GnRH 48h later (PGF+GnRH) and then reinsemination after detection of estrus (9 of 160) or at 16-20h after GnRH (151 of 160). Blood samples were collected at the time of the not-pregnant diagnosis and again 48h later. Concentrations of progesterone before treatment with PGF(2alpha) were elevated (<1ng/ml) in 61% of the cows when PGF(2alpha) was administered and 81% of the cows given PGF(2alpha) had low (<1ng/ml) concentrations of progesterone 48h after PGF(2alpha). Treated cows were re-inseminated earlier (P<0.01; 31+/-1days) after first-service TAI than controls (55+/-1days). Conception rates after treatment were not different among treatments: PGF (22%), PGF+GnRH (23%), and control (23%). Average intervals from calving to conception were 22-23 days less (P<0.001) in treated cows than in controls. We concluded that treating nonpregnant cows with PGF(2alpha) on Days 27-29 after insemination produced acceptable conception rates when inseminations were made after detected estrus or when TAI was used after GnRH treatment. Further, both treatments reduced days between first-service TAI and second inseminations, and days from calving to conception. 相似文献
84.
Structure and axon outgrowth inhibitor binding of the Nogo-66 receptor and related proteins 总被引:23,自引:0,他引:23 下载免费PDF全文
Barton WA Liu BP Tzvetkova D Jeffrey PD Fournier AE Sah D Cate R Strittmatter SM Nikolov DB 《The EMBO journal》2003,22(13):3291-3302
The myelin-derived proteins Nogo, MAG and OMgp limit axonal regeneration after injury of the spinal cord and brain. These cell-surface proteins signal through multi-subunit neuronal receptors that contain a common ligand-binding glycosylphosphatidylinositol-anchored subunit termed the Nogo-66 receptor (NgR). By deletion analysis, we show that the binding of soluble fragments of Nogo, MAG and NgR to cell-surface NgR requires the entire leucine-rich repeat (LRR) region of NgR, but not other portions of the protein. Despite sharing extensive sequence similarity with NgR, two related proteins, NgR2 and NgR3, which we have identified, do not bind Nogo, MAG, OMgp or NgR. To investigate NgR specificity and multi-ligand binding, we determined the crystal structure of the biologically active ligand-binding soluble ectodomain of NgR. The molecule is banana shaped with elongation and curvature arising from eight LRRs flanked by an N-terminal cap and a small C-terminal subdomain. The NgR structure analysis, as well as a comparison of NgR surface residues not conserved in NgR2 and NgR3, identifies potential protein interaction sites important in the assembly of a functional signaling complex. 相似文献
85.
David J. Shuey Maria Betty Philip G. Jones Xavier Z. Khawaja Mark I. Cockett 《Journal of neurochemistry》1998,70(5):1964-1972
Abstract: The RGS proteins are a recently discovered family of G protein regulators that have been shown to act as GTPase-activating proteins (GAPs) on the Gαi and Gαq subfamilies of the heterotrimeric G proteins. Here, we demonstrate that RGS7 is a potent GAP in vitro on Gαi1 and Gαo heterotrimeric proteins and that RGS7 acts to down-regulate Gαq -mediated calcium mobilization in a whole-cell assay system using a transient expression protocol. This RGS protein and RGS4 are reported to be expressed predominantly in brain, and in situ hybridization studies have revealed similarities in the regional distribution of RGS and Gαq mRNA expression. Our findings provide further evidence to support a functional role for RGS4 and RGS7 in Gαq -mediated signaling in the CNS. 相似文献
86.
87.
Kees L. de Visser Gijs W. D. Landman Betty Meyboom-de Jong Wim de Visser Gerard J. te Meerman Henk J. G. Bilo 《PloS one》2015,10(7)
IntroductionThe development of type 2 diabetes results from an interaction of hereditary factors and environmental factors. This study aimed to investigate the contribution of interrelatedness to the risk of developing type 2 diabetes in an isolated Dutch population.ResultsPatients with type 2 diabetes were more interrelated, expressed by a higher KC compared to controls (7.2 vs. 5.2, p=0.001). First, second and third degree relatives had an increased risk of developing type 2 diabetes. Second degree relatives had a similar risk,1.7 (1.5-2.0) as third degree relatives,1.8 (1.5-2.2). Spouses of patients with diabetes had a 3.4 (2.7-4.4) higher risk of developing type 2 diabetes.ConclusionsInterrelatedness was higher among inhabitants with type 2 diabetes compared to controls. This differences extended beyond the nuclear family, thereby supporting the hypothesis that interrelatedness contributed to the development of type 2 diabetes on Urk. However, the size of this effect was small and the patterns of risk in first, second and third degree relatives suggested that factors other than interrelatedness were the main contributors to the development of type 2 diabetes on Urk. 相似文献
88.
89.
Two new species of Scaphochlamys, S. krauensis Y. Y. Sam and S. pusilla Y. Y. Sam, from the Krau Wildlife Reserve, Pahang are described and illustrated. Another two Scaphochlamys species, S. pennipicta and S. oculata are also reported from Krau Wildlife Reserve, considerably extending their known distribution. An identification key for all four Scaphochlamys species found in the Krau Wildlife Reserve is provided. 相似文献
90.
Alternative reproductive tactics have been described in male mammals, but little information exists regarding fitness benefits
and whether males change tactics. Adult male prairie voles Microtus ochrogaster (Wagner, 1842) display alternative tactics described as resident and wanderer. Enclosure studies provide conflicting data
concerning the relative success of each tactic and whether males display one tactic throughout adulthood. To characterize
further residents and wanderers in this species, we examined data collected during 5 years of monitoring a natural population
in Illinois, USA. We found that during the breeding period, wandering males survived longer, moved longer distances, and were
more likely than residents to have scrotal testes. During the nonbreeding period, wandering and resident males differed only
in whether or not they established residency. Data on sources and fates of resident and wandering males revealed that a substantial
proportion of males switched tactics. Our estimate of the reproductive contribution of wandering males to the population,
which is based on the premise that wandering males typically mate with single females, suggests that wanderers contribute
34–38% of young recruited during March through October and 4–12% in November, when single females are less common. Parentage
studies in natural populations are necessary to test our estimates. 相似文献