全文获取类型
收费全文 | 4669篇 |
免费 | 338篇 |
国内免费 | 2篇 |
专业分类
5009篇 |
出版年
2023年 | 32篇 |
2022年 | 30篇 |
2021年 | 76篇 |
2020年 | 41篇 |
2019年 | 41篇 |
2018年 | 96篇 |
2017年 | 100篇 |
2016年 | 120篇 |
2015年 | 176篇 |
2014年 | 218篇 |
2013年 | 279篇 |
2012年 | 350篇 |
2011年 | 324篇 |
2010年 | 219篇 |
2009年 | 193篇 |
2008年 | 271篇 |
2007年 | 280篇 |
2006年 | 237篇 |
2005年 | 238篇 |
2004年 | 244篇 |
2003年 | 226篇 |
2002年 | 217篇 |
2001年 | 101篇 |
2000年 | 113篇 |
1999年 | 86篇 |
1998年 | 64篇 |
1997年 | 35篇 |
1996年 | 51篇 |
1995年 | 26篇 |
1994年 | 35篇 |
1993年 | 20篇 |
1992年 | 40篇 |
1991年 | 43篇 |
1990年 | 33篇 |
1989年 | 30篇 |
1988年 | 29篇 |
1987年 | 17篇 |
1986年 | 23篇 |
1985年 | 24篇 |
1984年 | 19篇 |
1983年 | 17篇 |
1982年 | 11篇 |
1981年 | 16篇 |
1980年 | 16篇 |
1979年 | 19篇 |
1978年 | 23篇 |
1977年 | 20篇 |
1976年 | 23篇 |
1973年 | 9篇 |
1971年 | 7篇 |
排序方式: 共有5009条查询结果,搜索用时 0 毫秒
1.
When fibrin polymerizes in a strong magnetic field, it can be highly oriented. The structural diffraction study of the oriented polymer becomes thus possible. The magnetic birefringence can also be used to study the development of the polymer Fibrinogen in solution is weakly oriented in high magnetic fields. In this work we present complementary results and discussion. The validity of the comparison of the orientation parameters of fibrinogen and fibrin with those of other orientable known biological structures is discussed. The orientation of fibrin formed from fibrin monomer solution is compared to that of fibrin formed by the action of thrombin on fibrinogen. The conditions to obtain highly oriented fibrin gels suitable for three dimensional structure studies are also briefly discussed. 相似文献
2.
The Murray River's 'Sea to Hume Dam' fish passage program: Progress to date and lessons learned 总被引:2,自引:0,他引:2
Since its commencement in 2001, a program to facilitate fish passage on a major stretch of Australia's longest river has installed eight structures, testing and modifying their design as they go. What are the results so far and what are the implications for future directions? 相似文献
3.
Three different fluorochrome and specific counterstain combination (DAPI/AMD, DA/DAPI and CMA/DA) treatments were applied to the chromosomes of four Microtidae (Rodentia) species. The results complete the data obtained in our previous paper (Burgos, M., Jiménez, R., & Dìaz de la Guardia, R., Genome 30:540–546, 1988) and prove that the changes in the constitutive heterochromatin in the evolution of the karyotypes of these species are not only due to gain or loss of heterochromatin, but are qualitative with respect to their nucleotide composition, repeated base pair organization or DNA-protein complex modification. These variations lead to the differential response to the fluorescence dye combinations used. 相似文献
4.
5.
Heavy metal residues in birds of Lake Nakuru, Kenya 总被引:1,自引:0,他引:1
Jim K. Kairu 《African Journal of Ecology》1996,34(4):397-400
6.
Nine-banded armadillosDasypus novemcinctus Linnaeus, 1758 are interesting in part because (a) they give birth to litters of genetically identical quadruplets, and (b) the species’ range has expanded rapidly throughout the southern United States during the last 150 years, suggesting substantial dispersal of individuals. Using data from 7 field seasons between 1992 and 1999, we examined the extent of juvenile recruitment and retention of adults in a population of armadillos from northern Florida. There were no sex differences in the likelihood of recruitment or most attributes of male and female recruits at any age. In the few cases where more than one littermate was recruited into the population, siblings were significantly more widely dispersed as adults than they were as juveniles, thus limiting opportunities for interaction among clonal siblings. There was some evidence that recruits ranged more widely than other individuals, suggesting recruits may have been searching for suitable sites to establish themselves. Recruits were heavier than non-recruits as both juveniles and yearlings, which may have aided in establishing a home range, but recruits were lighter than other animals as adults. Overall, slightly less than 50% of armadillos first captured as adults were never seen in a subsequent year, suggesting these individuals may have been transients. However, some adults remained in the population for multiple years, moving very little from the area where they were first sighted. As with recruits, there were no sex differences in the likelihood of adults being retained in the population nor in the attributes of retained males and females. Retained animals exhibited more extensive anatomical damage and moved farther between successive sightings within years than did non-residents. Adults were more likely to be retained in the population than juveniles were to be recruited, and retained adults were older, heavier, and exhibited more extensive anatomical damage than did recruits. Our data seem to indicate a population characterized by limited recruitment of juveniles (particularly of clonemates) and an adult population exhibiting considerable turnover from year to year, but with a core of individuals who are long-term residents. 相似文献
7.
Jim Orford 《BMJ (Clinical research ed.)》1988,296(6624):729-730
8.
9.
10.
Creatine kinase activity and its isoenzymatic profile in rat intestinal mucose during normal development have been studied. Creatine kinase enzymatic activity increased stepwise during fetal development and the first week of life. An isoenzymatic pattern of exclusively CK-BB types occurred in all segments of the digestive tract during the early fetal stage. The isoenzyme profile of creatine kinase in the esophagic tissue with advancing maturation of the fetus shifted in the same way as in adults, with preferential concentration of CK-MM. However, CK-BB continued to be the main isoenzyme in the rest of the digestive tract. Our results show that rats are particularly suitable for experimental studies of intestinal creatine kinase isoenzymes. 相似文献