全文获取类型
收费全文 | 3940篇 |
免费 | 345篇 |
国内免费 | 7篇 |
出版年
2023年 | 30篇 |
2022年 | 25篇 |
2021年 | 57篇 |
2020年 | 84篇 |
2019年 | 56篇 |
2018年 | 143篇 |
2017年 | 115篇 |
2016年 | 132篇 |
2015年 | 121篇 |
2014年 | 110篇 |
2013年 | 296篇 |
2012年 | 332篇 |
2011年 | 369篇 |
2010年 | 183篇 |
2009年 | 142篇 |
2008年 | 323篇 |
2007年 | 285篇 |
2006年 | 268篇 |
2005年 | 190篇 |
2004年 | 191篇 |
2003年 | 189篇 |
2002年 | 134篇 |
2001年 | 53篇 |
2000年 | 59篇 |
1999年 | 20篇 |
1998年 | 13篇 |
1997年 | 14篇 |
1996年 | 14篇 |
1995年 | 11篇 |
1994年 | 18篇 |
1993年 | 12篇 |
1992年 | 17篇 |
1991年 | 12篇 |
1989年 | 13篇 |
1988年 | 9篇 |
1987年 | 16篇 |
1986年 | 8篇 |
1985年 | 14篇 |
1984年 | 18篇 |
1983年 | 19篇 |
1982年 | 21篇 |
1981年 | 14篇 |
1980年 | 11篇 |
1979年 | 9篇 |
1978年 | 8篇 |
1977年 | 8篇 |
1976年 | 11篇 |
1975年 | 8篇 |
1973年 | 9篇 |
1972年 | 9篇 |
排序方式: 共有4292条查询结果,搜索用时 140 毫秒
1.
2.
The trend of increasing height can be interpreted as a reflection of the unfolding progress of civilization. Height changes among children and adolescents are good markers of this trend. We analyze the secular trend in the heights of children and adolescents in the Czech Republic on the basis of data from anthropological surveys. The earliest height data pertain to Czech youths who attended the Military Schools in Austria in 1800-1809. Data also exist for 1895 and continue in 1951 and at 10-year intervals thereafter. Growth curves were obtained for separate age groups by fitting mean values via third-order polynomial smoothing splines. Between 1951 and 2001, the mean heights of boys and girls aged 2.5 years increased by 2.7 and 3 cm, respectively. Since 1895, the mean height of 13-year-old boys has increased by 19.4 cm, and the mean height of girls has increased by 18.3 cm. 相似文献
3.
4.
Hana Votavová Vladimír Gut Karel Bláha Jaroslav Šponar 《International journal of biological macromolecules》1982,4(6):341-346
DNA complexes with polypeptides (Lys-Ala-Ala)1)] and (Lys-Ala-Ala)34 have been studied using the methods of thermal melting and circular dichroism. Derivative melting curves of (Lys-Ala-Ala)10 DNA differed substantially from those of (Lys-Ala-Ala)34 prepared either by salt gradient dialysis or by direct mixing. Melting curves of the former complex were unimodal or bimodal with Tm increasing continuously withn input lysin-to-DNA phosphate ratio (r); those of the latter complex consisted of three separate transitions with Tm values almost independent of r. Complete reversibility of binding in the (Lys-Ala-Ala)10-DNA system but a slow redistribution of (Lys-Ala-Ala)34 on DNA at low temperature were found in the redistribution experiments Much faster redistribution from denatured to native DNA occurs at the temperature of melting, contributing to the unusual trimodal melting pattern. Circular dichroism curves are very similar for both complexes and indicate little change of DNA conformation upon polypeptide binding. 相似文献
5.
Corynebacterium equi IFO 3730 was found to oxidize a wide variety of sec-alcohols, including alkanols, substituted alkanols, alkenols and cyclic alcohols, in moderate to high yields. Among them, the sec-alcohols which have longer carbon chains were oxidized more smoothly than those with smaller numbers of carbon. Although both enantiomers of unsymmetrically disubstituted carbinols were oxidized, the S form of 2-dodecanol was converted to the corresponding ketone a little faster than the other enantiomer. 相似文献
6.
7.
8.
Yosiaki Itô 《Journal of Ethology》1987,5(2):115-124
Social behaviour ofRopalidia revolutionalis (de Saussure) was observed in Brisbane and Townsville. Nests were, as a rule, founded by association of females. Each nest
began as a single comb but, after the emergence of progeny adults, satellite combs were constructed near the original comb.
During the pre-emergence (single-comb) stage, each colony had a single egg-layer, despite the rare occurrence of intranidal
dominance acts among female wasps. When colonies had reached the multiple-comb stage, the frequency and intensity of intranidal
dominance-aggressive acts rose to a high level, comparable to those of typically aggressive colonies of e.g.Polistes canadensis in Panama. Colonies appeared to be still functionally haplometrotic during the early phase of multiple-comb stage, but several
potential egg-layers were present as colony size increased. Dominant females often performed wing vibration, rapid runs between
combs and tended to sit on the largest comb, whilst subordinate females tended to sit on smaller combs. 相似文献
9.
C. R. Vonk E. Davelaar S. A. Ribôt B. Shadid H. C. Van der Plas 《Plant Growth Regulation》1989,8(3):263-276
It is shown that in bulbous Iris zeatin originates from a nucleotide. This nucleotide is probably zeatin-allylic-phosphate, in which a phosphate group is attached to the isoprenoid side-chain of zeatin. The formation of zeatin-allylic-phosphate from t-zeatin and 8-[14C]-zeatin by the microsomal fractions of Iris bulb disks and Helianthus tubers was demonstrated. The responsible enzyme was partially purified. 5-AMP was found to be a phosphate group delivering substrate. Adenosine and adenine inhibited the enzyme reaction. The significance of the results is discussed in relation to cytokinin biosynthesis and the occurrence of bud blast in Iris. 相似文献
10.
An engineered retroviral proteinase from myeloblastosis associated virus acquires pH dependence and substrate specificity of the HIV-1 proteinase.
下载免费PDF全文
![点击此处可从《The EMBO journal》网站下载免费的PDF全文](/ch/ext_images/free.gif)
J Konvalinka M Horejsí M Andrensky P Novek I Pichov I Blha M Fbry J Sedlcek S Foundling P Strop 《The EMBO journal》1992,11(3):1141-1144
In an attempt to understand the structural reasons for differences in specificity and activity of proteinases from two retroviruses encoded by human immunodeficiency virus (HIV) and myeloblastosis associated virus (MAV), we mutated five key residues predicted to form part of the enzyme subsites S1, S2 and S3 in the substrate binding cleft of the wild-type MAV proteinase wMAV PR. These were changed to the residues occupying a similar or identical position in the HIV-1 enzyme. The resultant mutated MAV proteinase (mMAV PR) exhibits increased enzymatic activity, altered substrate specificity, a substantially changed pH activity profile and a higher pH stability close to that observed in the HIV-1 PR. This dramatic alteration of MAV PR activity achieved by site-directed mutagenesis suggests that we have identified the amino acid residues contributing substantially to the differences between MAV and HIV-1 proteinases. 相似文献