全文获取类型
收费全文 | 6933篇 |
免费 | 689篇 |
出版年
2022年 | 40篇 |
2021年 | 99篇 |
2020年 | 57篇 |
2019年 | 63篇 |
2018年 | 72篇 |
2017年 | 71篇 |
2016年 | 152篇 |
2015年 | 276篇 |
2014年 | 299篇 |
2013年 | 334篇 |
2012年 | 470篇 |
2011年 | 466篇 |
2010年 | 280篇 |
2009年 | 266篇 |
2008年 | 384篇 |
2007年 | 334篇 |
2006年 | 331篇 |
2005年 | 349篇 |
2004年 | 333篇 |
2003年 | 319篇 |
2002年 | 352篇 |
2001年 | 122篇 |
2000年 | 102篇 |
1999年 | 94篇 |
1998年 | 98篇 |
1997年 | 62篇 |
1996年 | 61篇 |
1995年 | 67篇 |
1994年 | 64篇 |
1993年 | 63篇 |
1992年 | 64篇 |
1991年 | 68篇 |
1990年 | 83篇 |
1989年 | 71篇 |
1988年 | 74篇 |
1987年 | 70篇 |
1986年 | 65篇 |
1985年 | 87篇 |
1984年 | 88篇 |
1983年 | 72篇 |
1982年 | 60篇 |
1981年 | 69篇 |
1980年 | 59篇 |
1979年 | 63篇 |
1978年 | 45篇 |
1977年 | 55篇 |
1976年 | 50篇 |
1974年 | 46篇 |
1973年 | 41篇 |
1972年 | 39篇 |
排序方式: 共有7622条查询结果,搜索用时 15 毫秒
1.
A selective and diagnostic medium for ammonia oxidising bacteria 总被引:2,自引:0,他引:2
2.
Judith T. Irvine 《American anthropologist》1998,100(2):580-581
The Oral History and Literature of the Wolof People of Waalo, Northern Senegal. Samba Diop. Lewiston, Canada; Edwin Mellen Press, 1995. 389 pp. 相似文献
3.
Pancreatic islet homogenates contain a Mg2+-requiring phospholipid methyltransferase activity, the activity of which was doubled by calcium (K0.5 less than 5 microM). Other divalent metal ions stimulated the activity from 11 to 35%, but zinc and strontium were inhibitory. Cyclic AMP had no effect on the enzyme activity and cyclic GMP inhibited it slightly. Calcium increased the Vmax of the enzyme without affecting its Km with respect to S-adenosylmethionine (6 microM). Chlorpromazine, trifluoperazine, and dibucaine inhibited the calcium-stimulatable activity without affecting the activity in the absence of calcium. Phosphatidylserine stimulated, and arachidonic acid and palmitic acid inhibited, the basal enzyme activity. The methylated products were found to be primarily mono- and dimethylphosphatidylethanolamine (30%) and phosphatidylcholine (43%) and an, as yet unidentified, nonpolar lipid fraction (27%), as judged by thin-layer chromatography. In the presence of calcium, incorporation of methyl groups into phosphatidylcholine, mono- and dimethylphosphatidylethanolamine, and nonpolar lipids was increased by 131, 60, and 46%, respectively. Based on the localization of the enzyme activity in the insulin secretory granule fraction, it is proposed that phospholipid methylation plays a role in coupling the stimulus to the initial events in insulin secretion, leading to the exocytosis of insulin. 相似文献
4.
5.
F.J. Murillo B.W. MacDonald E. Kenchington S.E. Campana B. Sainte-Marie M. Sacau 《Marine Biology Research》2018,14(4):366-382
We examined four species of sea pen (Anthoptilum grandiflorum, Halipteris finmarchica, Pennatula aculeata and Pennatula grandis) collected from the Gulf of St. Lawrence and mouth of the Laurentian Channel, eastern Canada. An exponential length–weight relationship was found for all four species, where growth in weight was progressively greater than growth in length with increasing colony size. Halipteris finmarchica, P. grandis and P. aculeata presented the better allometric fits, explaining over 80% of the variance. In addition, a count of growth increments visible in transverse sections in 86 A. grandiflorum and 80 P. aculeata samples was made. Presumed ages ranged between 5 and 28 years for A. grandiflorum and 2 and 21 years for P. aculeata. Radiocarbon assays were inconclusive and could not be used to confirm these ages; further age validation is required. Radial growth of the rod is slow during the first years, increasing at intermediate sizes of the colony and slowing down again for large colonies. Similar results were obtained from the relationship between colony length and number of growth increments where a logistic model was the best fit to the data. On average Spearman’s rank correlations showed 11% of shared variance between sea pen length or weight and environmental variables. Bottom temperature and salinity, depth and summer primary production were significantly correlated to sea pen size for most species. 相似文献
6.
7.
Eileen M. Proctor Judith L. Isaac-Renton William B. Robertson William A. Black 《CMAJ》1985,133(9):876-878
A survey was done of Canadians who had been interned by the Japanese during World War II to assess the prevalence of latent infection with Strongyloides stercoralis in this group. Packages containing three mail-in kits and a questionnaire were sent to 992 men, 694 (70%) of whom responded. Larvae were found in the stool specimens of four of the respondents. Examination of stool specimens after formalin-ether concentration was the most successful method of detecting Strongyloides larvae. The Baermann concentration technique yielded negative results in all four men. Three of the four cases of strongyloidiasis were detected after sampling of three fecal specimens. In the fourth case additional specimens were requested on the basis of data derived from the questionnaire. The most frequently cited clinical manifestations were abdominal pain, weight loss, diarrhea and rashes. 相似文献
8.
The substantia nigra plays a pivotal role in the relay of output from the striatum. One neural pathway from substantia nigra projects GABAergic fibers to the caudal mesencephalic tegmentum, terminating in the vicinity of the pedunculopontine nucleus (PPN). To evaluate the functional importance of this projection in the mediation of stereotyped behaviors of striatal and nigral origin, we microinjected low doses of the GABA agonist, muscimol, bilaterally into the vicinity of the PPN. This muscimol treatment resulted in a total blockade of all stereotyped behaviors normally elicited by systemic apomorphine or by intranigral muscimol. Blockade was not observed in animals microinjected with muscimol into the dorsal reticular formation, 1 mm above the level of the PPN. Our results indicate that the nigrotegmental projection may play a crucial role in the expression of stereotyped and dyskinetic behaviors of basal ganglia origin. 相似文献
9.
10.