全文获取类型
收费全文 | 11893篇 |
免费 | 1072篇 |
国内免费 | 5篇 |
专业分类
12970篇 |
出版年
2023年 | 61篇 |
2022年 | 73篇 |
2021年 | 157篇 |
2020年 | 104篇 |
2019年 | 128篇 |
2018年 | 153篇 |
2017年 | 137篇 |
2016年 | 255篇 |
2015年 | 348篇 |
2014年 | 439篇 |
2013年 | 571篇 |
2012年 | 753篇 |
2011年 | 775篇 |
2010年 | 481篇 |
2009年 | 461篇 |
2008年 | 680篇 |
2007年 | 648篇 |
2006年 | 649篇 |
2005年 | 614篇 |
2004年 | 647篇 |
2003年 | 595篇 |
2002年 | 582篇 |
2001年 | 146篇 |
2000年 | 111篇 |
1999年 | 159篇 |
1998年 | 165篇 |
1997年 | 132篇 |
1996年 | 139篇 |
1995年 | 113篇 |
1994年 | 124篇 |
1993年 | 122篇 |
1992年 | 128篇 |
1991年 | 107篇 |
1990年 | 106篇 |
1989年 | 86篇 |
1988年 | 104篇 |
1987年 | 100篇 |
1986年 | 91篇 |
1985年 | 96篇 |
1984年 | 102篇 |
1983年 | 104篇 |
1982年 | 100篇 |
1981年 | 98篇 |
1980年 | 88篇 |
1979年 | 72篇 |
1978年 | 64篇 |
1977年 | 60篇 |
1976年 | 63篇 |
1974年 | 62篇 |
1973年 | 55篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
111.
112.
Douglas H. Sandberg 《The Western journal of medicine》1961,94(5):287-291
In considering drug therapy for pregnant women, it must be borne in mind that almost all chemical compounds in use as therapeutic agents pass from the maternal to the fetal circulation through the placenta. These drugs can produce a wide range of harmful effects on the fetus and neonatal infant. The effects of some substances for which we have data reflecting a deleterious effect are listed.It is suggested that in the future more caution be exercised in using drugs during pregnancy and that in histories, both obstetrical and pediatric, any therapy given to the mother during gestation be recorded in detail. 相似文献
113.
114.
115.
Douglas R. Dewey 《American journal of botany》1965,52(10):1039-1045
Five hybrids were obtained from 12 seeds formed in 26 emasculated florets of A. riparium pollinated by A. repens. The hybrid plants were morphologically intermediate between the parents for vegetative and spike characteristics, although they resembled A. repens more closely than A. riparium. The 28-chromosome A. riparium parent behaved cytologically as an allotetraploid and formed an average of 13.98 II and 0.04 I in 94 cells at metaphase I. An average of 20.27 II and 0.36 IV were observed at metaphase I in 55 cells of A. repens, which was designated as a segmental autoallohexaploid. The hybrids contained 35 chromosomes and averaged 6.75 I, 12.49 II, 1.05 III, 0.01 IV, and 0.01 V in 162 cells interpreted at metaphase I. Bivalent chromosome pairing in the hybrids was attributed to autosyndetic pairing of 2 A. repens genomes and allosyndetic pairing between 1 A. riparium genome and 1 A. repens genome. Multivalent chromosome associations were attributed to structural hybridity. A. repens and A. riparium apparently share a genome in common, and this genome is the one responsible for rhizomes in both species. A. riparium was given a genome formula of R2R2SS; whereas the A. repens genome formula was written as R1R1X1X1X2X2, and the hybrid genome formula was designated as R1R2X1X2S. The “S” genome of A. riparium was derived from A. spicatum, and the “R” genome is the genome shared by A. repens and A. riparium. The origin and distribution of the so-called “X” genomes of A. repens remain unknown. The hybrids produced from 3 to 10% stainable pollen; however, no seed was set on the hybrids during 2 years in the field. 相似文献
116.
117.
Douglas Hubble 《BMJ (Clinical research ed.)》1965,1(5445):1293-1295
118.
Elizabeth B. Gargus Douglas H. Robinson James K. Bubien Lawrence B. Bugaisky Dale J. Benos 《In vitro cellular & developmental biology. Plant》1989,25(5):435-441
Summary Six- and seven-day post-coitus (p.c.) rabbit embryos have been cultured in an attempt to establish a trophectodermal cell
line. Results indicate that cells with epithelial characteristics (i.e. positive staining for cytokeratin) will survive in
culture until Passage 3. At that time a fibroblastlike cell becomes predominant. In addition, we have found that the presence
of the inner cell mass is required for embryo explants often results in the development of cells that spontaneously contract.
These cells stain positively for myosin, which indicates that they may be precardiac cells. Maximum diastolic potential was
−59±1.2 mV and the threshold potential was −53±2.3 mV. Spontaneously contracting cells did not respond to atropine, acetylcholine,
epinephrine, isoproterenol, or propranolol. Action potential seems to be a result of an inward calcium current, because the
beating rate is decreased in a dose-related manner with the calcium channel blocker verapamil, whereas the voltage-sensitive
sodium channel blocker tetrodotoxin was without effect.
This work was supported by grants HD21302, HD07069, DK31091, and HL37320 from the National Institutes of Health, Bethesda,
MD, with additional support from a University of Alabama at Birmingham Cardviovascular Research and Training Center Award. 相似文献
119.
120.