全文获取类型
收费全文 | 14030篇 |
免费 | 1471篇 |
国内免费 | 18篇 |
出版年
2021年 | 139篇 |
2020年 | 83篇 |
2019年 | 130篇 |
2018年 | 148篇 |
2017年 | 162篇 |
2016年 | 280篇 |
2015年 | 443篇 |
2014年 | 509篇 |
2013年 | 632篇 |
2012年 | 863篇 |
2011年 | 857篇 |
2010年 | 587篇 |
2009年 | 533篇 |
2008年 | 785篇 |
2007年 | 820篇 |
2006年 | 737篇 |
2005年 | 764篇 |
2004年 | 743篇 |
2003年 | 756篇 |
2002年 | 749篇 |
2001年 | 209篇 |
2000年 | 191篇 |
1999年 | 199篇 |
1998年 | 231篇 |
1997年 | 173篇 |
1996年 | 168篇 |
1995年 | 151篇 |
1994年 | 158篇 |
1993年 | 161篇 |
1992年 | 170篇 |
1991年 | 173篇 |
1990年 | 164篇 |
1989年 | 155篇 |
1988年 | 118篇 |
1987年 | 130篇 |
1986年 | 138篇 |
1985年 | 153篇 |
1984年 | 143篇 |
1983年 | 139篇 |
1982年 | 150篇 |
1981年 | 153篇 |
1980年 | 156篇 |
1979年 | 111篇 |
1978年 | 100篇 |
1977年 | 85篇 |
1976年 | 84篇 |
1975年 | 84篇 |
1974年 | 86篇 |
1973年 | 85篇 |
1972年 | 74篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
2.
3.
C Johnston 《CMAJ》1992,146(8):1446-1447
4.
5.
Myoglobin (Mb) is the classic vertebrate oxygen-binding protein present in aerobic striated muscles. It functions principally in oxygen delivery and provides muscle with its characteristic red colour. Members of the Antarctic icefish family (Channichthyidae) are widely thought to be extraordinary for lacking cardiac Mb expression, a fact that has been attributed to their low metabolic rate and unusual evolutionary history. Here, we report that cardiac Mb deficit, associated with pale heart colour, has evolved repeatedly during teleost evolution. This trait affects both gill- and air-breathing species from temperate to tropical habitats across a full range of salinities. Cardiac Mb deficit results from total pseudogenization in three-spined stickleback and is associated with a massive reduction in mRNA level in two species that evidently retain functional Mb. The results suggest that near or complete absence of Mb-assisted oxygen delivery to heart muscle is a common facet of teleost biodiversity, even affecting lineages with notable oxygen demands. We suggest that Mb deficit may affect how different teleost species deal with increased tissue oxygen demands arising under climate change. 相似文献
6.
7.
W W Johnston 《Acta cytologica》1984,28(3):218-224
From the time of its introduction, in 1973, through November 1983, fine needle aspiration biopsy ( FNAB ) of the lung was used in the diagnostic evaluation of 1,015 patients at the Duke University Medical Center and Durham Veterans Administration Medical Center. A diagnosis of a primary lung cancer was established in 49.4% of the cases and malignant neoplasm metastatic to the lung in 14.1%; a benign diagnosis was made in 31.1% and an inconclusive one in 5.4%. In 123 patients in whom lung tissue was also available, cancer was correctly diagnosed by FNAB in 83.8%, not diagnosed by FNAB in 14.6% and incorrectly diagnosed in 1.6%. In 37 patients without cancer, FNAB detected an infectious organism or a specific morphologic type of inflammation (abscess and granuloma). 相似文献
8.
Abstract— 2-Hydroxy-, 2-chloro-, 2- and Cmethyl-GABA are linear competitive inhibitors of GABA uptake in rat brain slices. These analogues are thus potential substrates for the GABA transport system and possible'false transmitters'. 2-Hydroxy-GABA is the most potent inhibitor of GABA uptake yet described. No specific inhibitor of GABA uptake was revealed amongst the drugs tested. 相似文献
9.
P Kendall-Taylor K Hall D G Johnston R W Prescott 《BMJ (Clinical research ed.)》1982,285(6340):465-467
The effect of pergolide mesylate was studied in two previously untreated men with large prolactinomas and exceptionally high prolactin concentrations. The study was designed to determine whether pergolide would be effective in alleviating symptoms, correcting hormonal abnormalities and shrinking the tumour. Starting with 50 micrograms daily the dose of pergolide was slowly increased over 10 weeks to 1 mg once daily, when repeat assessment was performed. Both patients reported complete relief of symptoms, with no side effects. Serum prolactin concentration was suppressed to normal in both subjects, and evidence to suggest tumour shrinkage was observed. Pergolide appears to be effective treatment for men with large prolactinomas. 相似文献
10.
The gorgoniid Eugorgia is exclusively an eastern Pacific genus. It has a wide geographic and bathymetric range of distribution, found from California to Perú and extends down to 65 m deep. Two new species are herein described. The morphological characters were analyzed and illustrated by light and scanning electron microscopy. Eugorgia beebei
sp. n. can be distinguished by its white, ascending, sparse colony growth. Eugorgia mutabilis
sp. n. can be distinguished by its white colony that changes color after collection, and the conspicuous sharp-crested disc sclerites. From a morphological point of view the new species are related to the daniana-group, the rubens-group and the siedenburgae-group of Eugorgia; their affiliations, and the proposal of a new group are discussed. These new species increases the number of species in the genus to 15, and contribute to the knowledge of the eastern Pacific octocoral biodiversity. 相似文献