全文获取类型
收费全文 | 7955篇 |
免费 | 862篇 |
国内免费 | 3篇 |
出版年
2023年 | 27篇 |
2022年 | 105篇 |
2021年 | 184篇 |
2020年 | 90篇 |
2019年 | 132篇 |
2018年 | 167篇 |
2017年 | 144篇 |
2016年 | 221篇 |
2015年 | 395篇 |
2014年 | 412篇 |
2013年 | 506篇 |
2012年 | 679篇 |
2011年 | 659篇 |
2010年 | 425篇 |
2009年 | 425篇 |
2008年 | 506篇 |
2007年 | 515篇 |
2006年 | 463篇 |
2005年 | 417篇 |
2004年 | 435篇 |
2003年 | 342篇 |
2002年 | 314篇 |
2001年 | 77篇 |
2000年 | 64篇 |
1999年 | 80篇 |
1998年 | 91篇 |
1997年 | 53篇 |
1996年 | 38篇 |
1995年 | 43篇 |
1994年 | 47篇 |
1993年 | 33篇 |
1992年 | 41篇 |
1991年 | 33篇 |
1990年 | 41篇 |
1989年 | 38篇 |
1988年 | 35篇 |
1987年 | 34篇 |
1986年 | 30篇 |
1985年 | 36篇 |
1984年 | 29篇 |
1983年 | 21篇 |
1982年 | 23篇 |
1981年 | 25篇 |
1979年 | 23篇 |
1978年 | 17篇 |
1975年 | 20篇 |
1974年 | 30篇 |
1973年 | 24篇 |
1972年 | 16篇 |
1969年 | 14篇 |
排序方式: 共有8820条查询结果,搜索用时 31 毫秒
51.
52.
Synchronized Chinese hamster cells were irradiated in air and in nitrogen at various points in the cell cycle. The irradiations were carried out after flushing with air or nitrogen with the medium removed from the mono-layer of cells. Under these conditions the dose-modifying factor, or oxygen enhancement ratio, was between 2.0 and 2.3 for survival in asynchronous cells. The variation in x-ray sensitivity evident as the cell progresses through its cycle was not differentially affected by its state of oxygenation at the time of irradiation. The x-ray age-response curves for irradiation in air and in nitrogen were similar at each point, except for the dose-modifying factor. This was true not only for the cells of a normal short generation time (10 hours) subline of the V79 line but also for a longer generation time (with longer GC period) subline derived from a "small colony". The variation in radiosensitivity as the cell progresses through its cycle must therefore be due to factors other than change in oxygen tension within the cell. The fact that the same variation in x-ray sensitivity with age exists for hypoxic cells as for well-oxygenated cells has a bearing on the radiotherapy of tumors which contain cells at low oxygen tensions. 相似文献
53.
54.
The conversion of protoheme to heme a in Staphylococcus 总被引:3,自引:0,他引:3
55.
56.
Wayne W. Grody Deborah Klein Amy E. Dodson Rita M. Kern Paul B. Wissmann Barbara K. Goodman Patrick Bassand Bert Marescau Soo-Sang Kang James V. Leonard Stephen D. Cederbaum 《American journal of human genetics》1992,50(6):1281-1290
We have explored the molecular pathology in 28 individuals homozygous or heterozygous for liver arginase deficiency (hyperargininemia) by a combination of Southern analysis, western blotting, DNA sequencing, and PCR. This cohort represents the majority of arginase-deficient individuals worldwide. Only 2 of 15 homozygous patients on whom red blood cells were available had antigenically cross-reacting material as ascertained by western blot analysis using anti-liver arginase antibody. Southern blots of patient genomic DNAs, cut with a variety of restriction enzymes and probed with a near-full-length (1,450-bp) human liver arginase cDNA clone, detected no gross gene deletions. Loss of a TaqI cleavage site was identified in three individuals: in a homozygous state in a Saudi Arabian patient at one site, at a different site in homozygosity in a German patient, and in heterozygosity in a patient from Australia. The changes in the latter two were localized to exon 8, through amplification of this region by PCR and electrophoretic analysis of the amplified fragment after treatment with TaqI; the precise base changes (Arg291X and Thr290Ser) were confirmed by sequencing. It is interesting that the latter nucleotide variant (Thr290Ser) was found to lie adjacent to the TaqI site rather than within it, though whether such a conservative amino acid substitution represents a true pathologic mutation remains to be determined. We conclude that arginase deficiency, though rare, is a heterogeneous disorder at the genotypic level, generally encompassing a variety of point mutations rather than substantial structural gene deletions. 相似文献
57.
58.
59.
60.
R.Lucille Roberts Amy Zullo Eric A. Gustafson C.Sue Carter 《Hormones and behavior》1996,30(4):576-582
This experiment was designed to examine the hypothesis that perinatal manipulation of gonadal or adrenal steroids can alter the subsequent expression of juvenile parental (alloparenting) and affiliative behavior in prairie voles (Microtus ochrogaster). Corticosterone (PRECORT), testosterone (PRE-TP), or oil injections (PRESES) were given on Prenatal Days 12–20 or on Postnatal Days 1–6 (CORT6, TP6, or SES6, respectively). Alloparenting was reduced significantly in females in the CORT6 group and in males in the TP6 group. Sibling affiliative preferences were increased significantly in PRE-TP females and stranger preferences were increased in TP6 and CORT6 females. The results suggest timing is a critical factor determining whether hormones have a facilitative or inhibitory effect on alloparental and affiliative behavior in prairie voles. In this species, corticosterone and testosterone have similar organizational effects on affiliative behavior in females. Alloparental behavior is inhibited by postnatal corticosterone administration in females and by postnatal testosterone administration in males, whereas prenatal steroid administration had no significant effect on alloparenting in either gender. 相似文献