全文获取类型
收费全文 | 47399篇 |
免费 | 3354篇 |
国内免费 | 19篇 |
专业分类
50772篇 |
出版年
2024年 | 52篇 |
2023年 | 175篇 |
2022年 | 565篇 |
2021年 | 912篇 |
2020年 | 568篇 |
2019年 | 682篇 |
2018年 | 1027篇 |
2017年 | 906篇 |
2016年 | 1477篇 |
2015年 | 2320篇 |
2014年 | 2668篇 |
2013年 | 2979篇 |
2012年 | 3939篇 |
2011年 | 3778篇 |
2010年 | 2392篇 |
2009年 | 2185篇 |
2008年 | 3028篇 |
2007年 | 2909篇 |
2006年 | 2540篇 |
2005年 | 2356篇 |
2004年 | 2161篇 |
2003年 | 1864篇 |
2002年 | 1615篇 |
2001年 | 1301篇 |
2000年 | 1228篇 |
1999年 | 990篇 |
1998年 | 393篇 |
1997年 | 338篇 |
1996年 | 245篇 |
1995年 | 209篇 |
1994年 | 207篇 |
1993年 | 172篇 |
1992年 | 326篇 |
1991年 | 295篇 |
1990年 | 266篇 |
1989年 | 226篇 |
1988年 | 173篇 |
1987年 | 163篇 |
1986年 | 131篇 |
1985年 | 105篇 |
1984年 | 78篇 |
1983年 | 84篇 |
1982年 | 63篇 |
1981年 | 53篇 |
1980年 | 54篇 |
1979年 | 69篇 |
1978年 | 51篇 |
1977年 | 50篇 |
1976年 | 43篇 |
1974年 | 63篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
Phosphorylation and inactivation of acetyl-coenzyme A (CoA) carboxylase by acetyl-CoA carboxylase kinase in the presence of ATP and Mg2+ requires coenzyme A. Coenzyme A did not enhance the phosphorylation of alternative substrates of the carboxylase kinase such as protamine or histones. Analogs of coenzyme A were also effective in stimulating the inactivation of carboxylase. The KA of CoA for stimulated carboxylase inactivation was 25 microM. The presence of coenzyme A did not alter the Km of the carboxylase kinase for its substrates, ATP and acetyl-CoA carboxylase. Fluorescence binding studies showed that CoA binds to carboxylase but not to the kinase. The KD of CoA binding to carboxylase is 27 microM. These results indicate that coenzyme A, acting on acetyl-CoA carboxylase, may play an important role in the regulation of the covalent modification mechanism for acetyl-CoA carboxylase. 相似文献
62.
Y J Kim J Shuman M Sette A Przybyla 《Biochemical and biophysical research communications》1983,117(3):682-687
Phosphorylation of a 25 Kdalton nuclear stress protein from rat muscle was examined by two-dimensional gel electrophoresis and one-dimensional peptide mapping. These studies show that three 25 Kdalton stress proteins found in stressed rat myoblasts are actually the same protein with charge variation brought about by multiple phosphorylations. Furthermore, the predominant charge variant of 25 Kdalton protein found in cells is dependent on the intensity of the stress applied to cells. 相似文献
63.
Sundra S. Kim 《The Western journal of medicine》1983,139(6):885-891
The aging process is a fugue composed of innumerable themes; the theme of “ethnicity” is by far one of its more dominant. Due to the increasing incidence of chronic, progressive infirmity and acute, catastrophic illness, the elderly are thrust into direct contact with the health care systems of their society. The experiences of ethnic elders in American health care situations are fraught with conflict and mutual dissatisfaction with the physician-patient relationship. Both providers and consumers of health care services harbor differing culture-bound perceptions of health, illness and the healing process; these cultural beliefs define personal and professional needs and expectations and notions of how those needs are to be met by others. Both physicians and patients can enhance their communication and their compassion for one another by acknowledgment of cultural differences and by increased willingness to interpret motives and behavior within native context.It behooves us in medicine to examine the cultural traditions underlying our own attitudes, beliefs and values about the aged in a universal sense, as well as in a culturally specific sense, that we may gain insight that will be helpful in serving elderly persons more effectively, and in solving some of the problems inherent in the aging process. 相似文献
64.
Temperature-jump methods were used to study the kinetics of the helix to coil transition in three fragments of yeast tRNAPhe that share a common 5' terminus (the 5' end of the mature tRNA). Correlation of the extrapolated helix dissociation time constants with NMR exchange broadening results allows assignment of the structural basis of the optical melting transition in the fragments. The results confirm nuclear magnetic resonance findings on these fragments: the 5' 1/4 fragment has no helical structure; the 5' 1/2 fragment contains the D stem; and the 5' 3/5 fragment contains the D stem and the anticodon stem. These are the structures expected if sequential folding of the tRNA during biosynthesis were to occur. The D stem is the last helix to melt in the 5' 3/5 fragment. We suggest that structural elements in addition to the four Watson-Crick base pairs of the D-stem helix are responsible for the anomalously high Tm of that hairpin. 相似文献
65.
Enumeration and Identification of Bacillus cereus in Foods: I. 24-Hour Presumptive Test Medium 总被引:1,自引:1,他引:0
An egg yolk-polymyxin medium (KG) for rapid enumeration of Bacillus cereus is described. The test is presumptive in that differentiation of B. cereus (and closely related organisms) from other species is based on the formation of turbidity in the agar surrounding the colonies of the cereus group organisms. The medium is formulated to encourage sporulation and release of free spores for serological confirmatory tests within the 24-hr incubation period. The production of turbidity in egg yolk and free-spore production by 25 strains of B. cereus on KG agar were measured. The recovery of food poisoning strains of B. cereus inoculated into nonsterile food slurries was assessed. A comparison of KG agar and mannitol-egg yolk-polymyxin-agar indicated that the two media were comparable in their abilities to recover low levels of B. cereus from naturally contaminated foods. Since KG agar enhances spore formation by B. cereus, thus permitting early serological testing, its use in screening food products is advocated. 相似文献
66.
New Class of Streptomycin-Resistant Mutants Incompatible with supX Suppressor Mutations in Salmonella typhimurium 总被引:1,自引:0,他引:1
Streptomycin-resistant colonies of Salmonella typhimurium appearing in platings of supX suppressors of strain leu-500 are less variegated in size than are those derived from strain leu-500 counterparts. Several of the streptomycin-resistant leu-500 clones, furthermore, yield suppressors and revertants of the leu-500 auxotrophy at unusually low rates, suggesting that they provide a genetic background inimicable to supX suppression. Two such "suppression-restrictive" leu-500 streptomycin-resistant (str) mutants, designated strains M(1) and M(4), were characterized as to their ability to receive the trp-supX-cysB linkage region by transduction. Coentry of a donor supX deletion mutation with the selected trp(+) marker was not observed even though these sites display more than 10% linkage in control experiments. This was demonstrably the result of nonviability of the combined supX mutant, M(1) or M(4) streptomycin-resistant genotype, rather than the lack of suppression of the leu-500 imparted auxotrophy. Both M(1)- and M(4)-type resistance was accompanied by pleiotropic effects resembling those caused by strB (nonribosomal)- rather than strA (ribosomal)-type resistance, but both restrictive mutants had a high upper limit of resistance corresponding to that of strA-type mutants. Transduction analyses indicated that the str character of neither the M(1) nor the M(4) strain was linked to the strA or the strB gene. These mutations define a previously undescribed locus, which we propose to designate strC, apparently related to streptomycin uptake rather than its intracellular action. Mutation at this locus is evidently incompatible with the inactivation or removal of the supX site, suggesting a functional association between products of the genes. 相似文献
67.
68.
69.
70.
The inhibiting effect of 14 typical creosote compounds on the aerobic degradation of toluene was studied in batch experiments. Four NSO-compounds (pyrrole, 1-methylpyrrole, thiophene, and benzofuran) strongly inhibited the degradation of toluene. When the NSO-compounds were present together with toluene, little or no degradation of toluene was observed during 16 days of incubation, compared with a total removal of toluene within 4 days when the four compounds were absent. Indole (an N-compound) and three phenolic compounds (phenol, o-cresol, and 2,4-dimethylphenol) also inhibited the degradation of toluene, though the effect was much weaker that of the four NSO-compounds. O-xylene, p-xylene, naphthalene and 1-methylnaphthalene seemed to stimulate the degradation even though the influence was very weak. No effects of benzothiophene (an S-compound) and quinoline (an N-compound) were observed. Benzofuran (an O-compound) was identified as the compound that most inhibited the degradation of toluene. An effect could be detected even at low concentrations (40 g/l).Abbreviations bf
benzofuran
- bt
benzothiophene
- dmp
2,4-dimethylphenol
- GC
gas chromatograph
- ind
indole
- mnap
1-methylnaphthalene
- MAH
monoaromatic hydrocarbons
- mpyr
1-methylpyrrole
- nap
naphthalene
-
o-cre
o-cresol
-
o-xyl
o-xylene
- phe
phenol
- pyr
pyrrole
-
p-xyl
p-xylene
- tol
toluene
- thi
thiophene
- qui
quinoline 相似文献