全文获取类型
收费全文 | 676857篇 |
免费 | 82723篇 |
国内免费 | 429篇 |
出版年
2016年 | 7632篇 |
2015年 | 11420篇 |
2014年 | 13023篇 |
2013年 | 18430篇 |
2012年 | 20927篇 |
2011年 | 21087篇 |
2010年 | 14088篇 |
2009年 | 13139篇 |
2008年 | 18624篇 |
2007年 | 19297篇 |
2006年 | 17762篇 |
2005年 | 17511篇 |
2004年 | 17118篇 |
2003年 | 16733篇 |
2002年 | 15983篇 |
2001年 | 29207篇 |
2000年 | 29505篇 |
1999年 | 23650篇 |
1998年 | 8660篇 |
1997年 | 9055篇 |
1996年 | 8729篇 |
1995年 | 8285篇 |
1994年 | 8383篇 |
1993年 | 8237篇 |
1992年 | 19726篇 |
1991年 | 18915篇 |
1990年 | 18405篇 |
1989年 | 18223篇 |
1988年 | 16639篇 |
1987年 | 16342篇 |
1986年 | 15052篇 |
1985年 | 14964篇 |
1984年 | 12641篇 |
1983年 | 11165篇 |
1982年 | 8839篇 |
1981年 | 8228篇 |
1980年 | 7564篇 |
1979年 | 12411篇 |
1978年 | 9672篇 |
1977年 | 9092篇 |
1976年 | 8601篇 |
1975年 | 9231篇 |
1974年 | 9930篇 |
1973年 | 9802篇 |
1972年 | 8945篇 |
1971年 | 8223篇 |
1970年 | 7058篇 |
1969年 | 6932篇 |
1968年 | 6162篇 |
1967年 | 5461篇 |
排序方式: 共有10000条查询结果,搜索用时 78 毫秒
41.
Maternal serum alpha-fetoprotein screening activities of state health agencies: a survey. 总被引:5,自引:5,他引:0 下载免费PDF全文
Maternal serum alpha-fetoprotein (MSAFP) screening has been demonstrated to be cost-effective on a population basis and is becoming standard practice. The American Society of Human Genetics has twice published policy statements to define the essential elements of a quality screening program. The present study reviewed the impact of these policy statements on state public-health agencies with respect to regulation or provision of MSAFP screening in their jurisdictions. With a few exceptions, states have not elected to play a major role in provision or regulation of this test. There is need to address issues of funding, standards, and data collection in a collaborative effort, if policy statements on genetic services are to be translated into effective state population screening. 相似文献
42.
43.
This is the first report of the growth in culture of Porphyra subtumens J. Agardh ex Laing (Bangiales, Rhodophyta), an obligate epiphyte of Durvillaea species and endemic to New Zealand waters. Archeospores, previously observed on field material, develop directly into the blade phase. Spores released from field collected blades form conchocelis. Conchospores develop into new blades, completing the life history in culture. Earlier reports of reproduction in P. subtumens gave conflicting accounts with some authors citing this species as having an asexual, monophasic life history with an unusual form of spore production, while others described spermatangia and carposporangia on the blade phase. 相似文献
44.
Ubiquity of Cysteine- and Metalloproteinase Activities in a Wide Range of Trypanosomatids 总被引:1,自引:0,他引:1
MARTA H. BRANQUINHA ALANE B. VERMELHO SAMUEL GOLDENBERG MYRNA C. BONALDO 《The Journal of eukaryotic microbiology》1996,43(2):131-135
We have analysed the proteinase profiles of 11 species from 7 different genera of trypanosomatids by in situ detection of enzyme activities on SDS-PAGE gels containing co-polymerized gelatin as substrate, and the use of specific proteinase inhibitors. Our survey indicates that while cysteine- and metalloproteinases are distributed ubiquitously among trypanosomatids, there are marked differences between the enzyme profiles from the monogenetic (Crithidia, Herpetomonas, Leptomonas) and digenetic (Trypanosoma, Endotrypanum, Phytomonas, Leishmania) species. The detected metalloproteinase activities, ranging in size from 50–100 kDa, partitioned into the detergent-phase after Triton X-114 extraction, while most of cysteine proteinases, of three distinct molecular mass ranges (30–50 kDa, 80–100 kDa and 116–205 kDa), partitioned into the aqueous phase. Thus, within this group of organisms, the metalloproteinase activities seem to be predominantly membrane-associated proteins. We also show that the plant parasites of the genus Phytomonas exhibit a distinctive cysteine proteinase profile that might be exploited further as a criterion for taxonomy of the genus. 相似文献
45.
46.
47.
48.
49.
50.