全文获取类型
收费全文 | 11109篇 |
免费 | 1003篇 |
国内免费 | 1篇 |
出版年
2022年 | 109篇 |
2021年 | 197篇 |
2020年 | 113篇 |
2019年 | 150篇 |
2018年 | 195篇 |
2017年 | 155篇 |
2016年 | 270篇 |
2015年 | 498篇 |
2014年 | 539篇 |
2013年 | 613篇 |
2012年 | 840篇 |
2011年 | 764篇 |
2010年 | 511篇 |
2009年 | 465篇 |
2008年 | 698篇 |
2007年 | 650篇 |
2006年 | 597篇 |
2005年 | 605篇 |
2004年 | 589篇 |
2003年 | 572篇 |
2002年 | 506篇 |
2001年 | 112篇 |
2000年 | 91篇 |
1999年 | 102篇 |
1998年 | 170篇 |
1997年 | 121篇 |
1996年 | 120篇 |
1995年 | 111篇 |
1994年 | 94篇 |
1993年 | 71篇 |
1992年 | 86篇 |
1991年 | 69篇 |
1990年 | 79篇 |
1989年 | 61篇 |
1988年 | 76篇 |
1987年 | 57篇 |
1986年 | 65篇 |
1985年 | 70篇 |
1984年 | 81篇 |
1983年 | 59篇 |
1982年 | 61篇 |
1981年 | 72篇 |
1980年 | 56篇 |
1979年 | 56篇 |
1978年 | 53篇 |
1977年 | 47篇 |
1976年 | 38篇 |
1974年 | 40篇 |
1973年 | 42篇 |
1970年 | 33篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
251.
252.
253.
Cytochromes c
3 of different strains of sulfatereducing bacteria have been purified and tested for their capacity to reduce colloidal sulfur to hydrogen sulfide. The results are in good agreement with the activities reported for the whole cells. Cytochrome c
3 is the sulfur reductase of some strains of sulfate-reducing bacteria such as Desulfovibrio desulfuricans Norway 4 and sulfate-reducing bacterium strain 9974 from which the sulfur reductase activity can be purified with the cytochrome c
3. In contrast, Desulfovibrio vulgaris Hildenborough cytochrome c
3 is inhibited by the product of the reaction namely hydrogen sulfide. Chloramphenicol has no effect on the sulfur reductase activity of D. desulfuricans Norway 4 when resting cells grown on lactate-sulfate medium are put in the presence of colloidal sulfur. This shows that the sulfur reductase activity is constitutive and corresponds to the fact that colloidal sulfur grown cells do not contain more cytochrome c
3 (or another sulfur reductase) than lactate-sulfate-grown cells. 相似文献
254.
Berenice M. Thomason Patricia P. Harris Karen R. Lewallen Roger M. McKinney 《Current microbiology》1979,2(6):357-360
A polyvalent conjugate forLegionella pneumophila, the Legionnaires’ disease bacterium, was prepared by combining monospecific antibodies for the four recognized serogroups
ofL. pneumophila. Pure cultures ofL. pneumophila and other bacteria representing 18 genera and 50 species of heterologous organisms were used in evaluating the reagent. A
total of 358 specimens from patients suspected of having Legionnaires’ disease also were tested. The results show the practicality
and advantages of using a polyvalentL. pneumophila conjugate for screening clinical specimens. 相似文献
255.
Jeffrey B. Krahling Robert Gee Patricia A. Murphy James R. Kirk N.E. Tolbert 《Biochemical and biophysical research communications》1978,82(1):136-141
Oxygen uptake with succinate or palmitoyl-CoA as substrates can be measured in rat liver mitochondria that have been isolated by sucrose density gradient centrifugation providing the fractions are diluted with a 30 mM phosphate buffer rather than with an isotonic medium. Separate assay procedures were used to measure peroxisomal and mitochondrial β-oxidation of palmitoyl-CoA in the fractions of a sucrose gradient used to separate these organelles. A preliminary estimate of the ratio of palmitoyl-CoA oxidation by the mitochondrial fraction relative to the surviving peroxisomes from livers of male rats was 3.2. 相似文献
256.
The distribution pattern of silver-NORs was studied in cells of six-day blastocysts and kidney fibroblasts of the rabbit using
the Ag-AS technique. At metaphase and interphase there was a binomial distribution of the number of stained sites in both
populations but blastocysts had a greater percentage of cells with larger numbers of stained sites. Up to 7 of the 8 chromosomes
known to bear NORs were stained in cells from blastocysts while a maximum of 6 were stained in fibroblasts. A significant
difference was found between the mean numbers of chromosomal NORs per cell in metaphases from blastocysts and fibroblasts,
where they were 4.2 and 3.3 respectively. Similarly, the mean number of NORs in interphase was significantly greater in cells
from blastocysts. The distribution of staining on chromosome pair 13 was related to cell type. Significantly more cells in
blastocysts than fibroblasts showed staining in this chromosome pair. 相似文献
257.
The specific activity of the enzyme choline acetyl transferase (CAT) in chick neuroretinas was investigated during in ovo development and in monolayer cultures. The enzyme activity was barely detectable on the 6th day of incubation but increased markedly between the 7th and 11th days. The activity increased sharply between the 15th and 17th days and then slowly until hatching. When cell suspensions from 6- to 7-day neuroretinas were cultured as monolayers, CAT specific activity increased rapidly. After 4–5 days in culture, the activity of the enzyme was identical to that found in the neuroretina on the 11th day of incubation. Cells from 9-day neuroretinas also differentiate in monolayer cultures, but with a more irregular pattern. These data show that cholinergic neurons from chick embryo neuroretina differentiate in monolayer cultures without a lag and at the same rate as in vivo. 相似文献
258.
Summary With the use of neutral sucrose sedimentation techniques, the size of unirradiated nuclear DNA and the repair of double-strand breaks induced in it by ionizing radiation have been determined in both wild-type and homozygous rad52 diploids of the yeast Saccharomyces cerevisiae. The number average molecular weight of unirradiated DNA in these experiments is 3.0×108±0.3 Daltons. Double-strand breaks are induced with a frequency of 0.58×10-10 per Daltonkrad in the range of 25 to 100 krad. Since repair at low doses is observed in wild-type but not homozygous rad52 strains, the corresponding rad52 gene product is concluded to have a role in the repair process. Cycloheximide was also observed to inhibit repair to a limited extent indicating a requirement for protein synthesis. Based on the sensitivity of various mutants and the induction frequency of double-strand breaks, it is concluded that there are 1 to 2 double-strand breaks per lethal event in diploid cells incapable of repairing these breaks. 相似文献
259.
The red marine algae Microcladia borealis, M. californica and M. coulteri produce several unusual halogenated monoterpenes including violacene, plocamene-B, plocamene-C, and plocamane-D. The isolation of these terpenes along with a study of their variation in each Microcladia at different locations are described. 相似文献
260.