全文获取类型
收费全文 | 11092篇 |
免费 | 1103篇 |
国内免费 | 5篇 |
出版年
2023年 | 70篇 |
2022年 | 119篇 |
2021年 | 328篇 |
2020年 | 159篇 |
2019年 | 202篇 |
2018年 | 265篇 |
2017年 | 233篇 |
2016年 | 379篇 |
2015年 | 603篇 |
2014年 | 676篇 |
2013年 | 803篇 |
2012年 | 876篇 |
2011年 | 956篇 |
2010年 | 571篇 |
2009年 | 448篇 |
2008年 | 680篇 |
2007年 | 670篇 |
2006年 | 555篇 |
2005年 | 495篇 |
2004年 | 467篇 |
2003年 | 373篇 |
2002年 | 356篇 |
2001年 | 132篇 |
2000年 | 128篇 |
1999年 | 106篇 |
1998年 | 89篇 |
1997年 | 67篇 |
1996年 | 64篇 |
1995年 | 76篇 |
1994年 | 50篇 |
1993年 | 42篇 |
1992年 | 62篇 |
1991年 | 61篇 |
1990年 | 67篇 |
1989年 | 56篇 |
1988年 | 57篇 |
1987年 | 68篇 |
1986年 | 63篇 |
1985年 | 40篇 |
1984年 | 63篇 |
1983年 | 37篇 |
1982年 | 33篇 |
1981年 | 48篇 |
1980年 | 35篇 |
1979年 | 33篇 |
1978年 | 35篇 |
1977年 | 31篇 |
1976年 | 33篇 |
1975年 | 35篇 |
1972年 | 27篇 |
排序方式: 共有10000条查询结果,搜索用时 156 毫秒
51.
52.
R D Adam 《Nucleic acids research》1992,20(12):3057-3061
Giardia lamblia trophozoites contain at least five sets of chromosomes that have been categorized by chromosome-specific probes. Pulsed field separations of G. lamblia chromosomes also demonstrated minor bands in some isolates which stained less intensely with ethidium than the major chromosomal bands. Two of the minor bands of the E11 clone of the ISR isolate, MBa and MBb, were similar to each other and to chromosomal band I by hybridization to total chromosomal DNA and by hybridization of specific probes. In order to determine the extent of this similarity, I have developed a panel of probes for many of the Pacl restriction fragments and have shown that most of the Pacl and Notl fragments found in MBa are also present in MBb. The differences are found in both telomeric regions. At one end, MBb contains a 300 kb region not found in MBa. At the other end of MBb is a 160 kb region containing the rDNA repeats which is bounded on one end by the telomeric repeat and on the other by sites for multiple enzymes that do not digest the rDNA repeats. The corresponding region of MBa is 23 kb in size. The size difference is consistent with the eightfold greater number of rDNA repeats in MBb than MBa and suggests that 30% of the size difference is accounted for by different numbers of copies of the rDNA repeat. MBa of another ISR clone (ISR G5) is 150 kb larger in size than MBa of ISR E11. The data suggest that MBa and MBb are homologous chromosomes of different sizes and that a portion of the size difference is accounted for by different copy numbers of the rDNA repeat. 相似文献
53.
Corticotropin releasing factor (CRF) both stimulates ACTH secretion from the pituitary and inhibits secretion of growth hormone (GH) in adult rats through actions in the CNS. The purpose of the present study was to evaluate these pituitary and central actions of CRF in neonatal rats, in which the hypothalamo- pituitary adrenal (HPA) axis is relatively hypo-functional. The results of this study show that central or peripheral administration of CRF evokes a marked dose-related rise in serum corticosterone in 6-day old rats. The same doses of CRF stimulate, rather than inhibit GH secretion. These results suggest that CRF has unique central actions early in ontogeny. 相似文献
54.
55.
Triterpene glycosides from Schefflera octophylla. 总被引:1,自引:0,他引:1
In addition to 3-epi-betulinic acid, three triterpene glycosides were isolated from leaves of Schefflera octophylla. The structures of the glycosides have been determined as 28-O-[alpha-L-rhamnopyranosyl(1----4)-O-beta-D-glucopyranosyl(1----6)-be ta-D- glucopyranosides of 3 alpha-hydroxy-lup-20(29)-ene-23,28-dioic acid, 3 alpha,11 alpha- dihydroxy-lup20(29)-ene-23,28-dioic acid and 3-epi-betulinic acid by spectroscopic data and chemical transformations. The last two compounds were found for the first time in the plant kingdom. 相似文献
56.
57.
58.
Purification, properties and cation activation of galactosyltransferase from lactating-rat mammary Golgi membranes 总被引:1,自引:0,他引:1
N Navaratnam S Ward C Fisher N J Kuhn J N Keen J B Findlay 《European journal of biochemistry》1988,171(3):623-629
Galactosyltransferase was purified from Golgi membranes of lactating-rat mammary gland and studied with respect to its physical and enzymic (lactose synthetase) properties. The enzyme occurred in both monomeric (43-46 kDa) and apparently dimeric (90 kDa) forms. It was very unstable except in the presence of phospholipid, detergent, or cations binding to site 2. The amino acid composition and the N-terminal sequence closely resembled that of the human and bovine milk enzymes, particularly in respect to a Pro-Pro-Pro-Pro sequence. Kinetic studies demonstrated a high-affinity Mn2+-binding site (1) essential for activity, and a low-affinity Mn2+-binding site (2) that could also bind spermidine or clupeine. Mn2+ binding at site 2 raised Vmax fivefold. Spermidine binding at site 2 enhanced Mn2+ binding at site 1, and influenced binding of glucose. At physiological glucose concentration, clupeine or spermidine activated nearly as well as 15 mM MnCl2 and are regarded as models of a natural cation activator that remains to be isolated. Evidence is given for an essential histidine residue in the galactosyltransferase. It is proposed that site 1 Mn2+ participates directly in the reaction mechanism, whereas site 2 is a regulator site allosterically activated by a basic protein. 相似文献
59.
Paternal Imprinting of Inversion Uab(1) Causes Homeotic Transformations in Drosophila 总被引:1,自引:0,他引:1
下载免费PDF全文
![点击此处可从《Genetics》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Paternal transmission of the bithorax-complex (BX-C) rearrangement, inversion Uab(1), causes a specific dominant gain of function phenotype in most abdominal segments. This represents a case of paternal imprinting since the mutant phenotype will occur only if inversion Uab(1) is paternally transmitted. The transformations in males are toward genital arch tissue. For females the transformations are to tissue found on abdominal segment 7 (Ab7) and to structures normally restricted to the genital disc. Ninety-six percent of transformed areas appear on Ab5 and Ab6 in both sexes and on Ab7 in females, coinciding with the Abd-B domain. Four percent of the transformations occurred on Ab1 through Ab4, coinciding with the abd-A domain. The mutant phenotype can be dramatically enhanced by modifying genes such as the posterior BX-C mutant tuh-3. Expressivity is modulated by maternal effect alleles interacting with tuh-3. A region of function within inversion Uab(1) appears to be programmed during spermatogenesis to function in a legacy dependent manner during embryogenesis. 相似文献
60.