全文获取类型
收费全文 | 3781篇 |
免费 | 316篇 |
国内免费 | 606篇 |
出版年
2024年 | 10篇 |
2023年 | 94篇 |
2022年 | 126篇 |
2021年 | 151篇 |
2020年 | 149篇 |
2019年 | 190篇 |
2018年 | 129篇 |
2017年 | 142篇 |
2016年 | 138篇 |
2015年 | 156篇 |
2014年 | 206篇 |
2013年 | 278篇 |
2012年 | 170篇 |
2011年 | 208篇 |
2010年 | 147篇 |
2009年 | 210篇 |
2008年 | 191篇 |
2007年 | 213篇 |
2006年 | 234篇 |
2005年 | 212篇 |
2004年 | 175篇 |
2003年 | 196篇 |
2002年 | 179篇 |
2001年 | 142篇 |
2000年 | 101篇 |
1999年 | 108篇 |
1998年 | 66篇 |
1997年 | 61篇 |
1996年 | 40篇 |
1995年 | 33篇 |
1994年 | 21篇 |
1993年 | 16篇 |
1992年 | 20篇 |
1991年 | 9篇 |
1990年 | 13篇 |
1989年 | 14篇 |
1988年 | 9篇 |
1987年 | 13篇 |
1986年 | 8篇 |
1985年 | 30篇 |
1984年 | 30篇 |
1983年 | 9篇 |
1982年 | 14篇 |
1981年 | 10篇 |
1980年 | 3篇 |
1979年 | 11篇 |
1978年 | 10篇 |
1976年 | 4篇 |
1973年 | 1篇 |
1950年 | 1篇 |
排序方式: 共有4703条查询结果,搜索用时 31 毫秒
951.
A cDNA clone encoding porcine α-lactalbumin (αLA) was isolated and sequenced. The longest clone was 688 nucleotides (nt) long and encoded a preprotein of 141 amino acids (aa) including a leader peptide of 19 aa. The porcine cDNA exhibited a nt similarity of between 72.2%–83.5% to other αLA cDNAs and an aa similarity of between 50.8%–85.2% with other αLA aa sequences. The derived aa sequence varied at three positions from a previously reported sequence for porcine αLA obtained by direct aa sequencing. 相似文献
952.
Juan E. Suárez JoséL. Caso Ana Rodriguez Carlos Hardisson 《FEMS microbiology letters》1984,22(2):113-117
Abstract Some structural characteristics of the Streptomyces phage φC31 were analyzed. A simpler and at least 50 times more efficient method than those previously described for isolating the phage is reported. The phage is naked, showing a polyhedral head 53 nm wide, a long non-contractile tail 100 × 5 nm, a basal plate 15 nm in diameter with at least one pin, and a prominent knot between the head and the tail. Up to 17 polypeptides had been found in the virion. Four of them, of 51, 38.5, 29.5 and 28 kDa, make up around 84% of the total protein of the particle. 相似文献
953.
R. G. LOXTON 《Zoological Journal of the Linnean Society》1979,65(1):103-110
Display behaviour in a small species of Indian praying mantis, Ephestiasula amoena , is described and the possible role of this display in courtship is discussed. The display involves exposure of the bright pattern on the inside face of the expanded plate-like profemora. The profemoral patterns found in closely related species are discussed and it is suggested that the display may also play a role in species recognition. The courtship behaviour of E. amoena is contrasted and compared with the courtship of other species of praying mantis. 相似文献
954.
Francis Paine Conant 《Human ecology: an interdisciplinary journal》1994,22(3):405-413
Four predictions are made on the future of space age technologies in human and cultural ecology: first, remote sensing systems will generate a need for more fieldwork, not less; second, the services and skills of anthropologists will become essential to the interpretation of satellite data, especially as these relate to areas characterized by non-Western cultural practices; third, training in remote sensing and the use of geographic information systems will become a regular offering for anthropology students; and fourth, since these new systems and methods can be applied retrospectively to the re-analysis of earlier ethnographic works, space age technologies will be with us for some time to come. 相似文献
955.
956.
The basic physical, chemical and physiological properties of a group II cholera phage belonging to Mukerjee's classification has been described. 相似文献
957.
S. Boinski 《American journal of primatology》1988,14(2):177-179
In Parque Nacional Manuel Antonio, Costa Rica, an adult male Cebus capucinus was observed repeatedly hitting a venomous snake (Bothropsasper) with a branch. Initially a large dead branch overhanging the snake had been broken off in the course of aggressive displays to the snake by the adult and two subadult males. The snake's escape was apparently prevented by the weight of the fallen branch and possibly by the injuries caused by its fall. This is the first direct observation of a capuchin monkey in a natural habitat using a tool. 相似文献
958.
Raji Padmanabhan Christopher D. Corsico Tazuko H. Howard Wolfgang Holter C. Michael Fordis Mark Willingham Bruce H. Howard 《Analytical biochemistry》1988,170(2):341-348
A method was developed to purify transiently transfected HeLa cells or African green monkey kidney CV-1 cells by magnetic affinity cell sorting. Monolayer cultures were transfected with mammalian expression vectors coding for either of two novel cell surface antigens, the Tac subunit of the human IL-2 receptor or vesicular stomatitis virus G protein. During the transient expression phase, cell populations were placed in suspension and mixed with monoclonal-antibody-coated magnetic particles in the presence of a sorting solution designed to minimize nonspecific cell/cell and cell/particle interactions. Transfected cells expressing the vector-encoded cell surface antigen were then isolated by application of a magnetic field. Reconstruction experiments indicated that IL-2 receptor-positive cells were bound about 100-fold more efficiently than receptor-negative cells. In transient transfection experiments, populations of greater than 90% antigen-positive cells were reproducibly obtained. 相似文献
959.
960.
《L'Anthropologie》2022,126(1):102974
Prehistoric sites testifying to human presence older than one million years in Europe are rare, and in the current state of knowledge, the oldest of them have been dated to around 1.4–1.5 Ma. The Vallonnet cave at Roquebrune-Cap-Martin in the Alpes-Maritimes, on the Mediterranean border, is one of the oldest sites in France to have yielded evidence of human activity: a lithic assemblage of about a hundred pieces and traces of butchery on bones of an Epivillafranchian fauna. The archaeological levels of this small cave were recently dated between 1.1 and 1.2 Ma by U-Pb correlated with paleomagnetic data. The site was occupied alternately by large carnivores that used it as a den or a lair, and by hominins that stayed there briefly in bivouac. The lithic remains are mainly percussion tools, shaped pebbles, flakes and cores, whose raw materials are local, or even semi-local, and on the whole not very diversified with mainly limestone, and to a lesser extent sandstone, quartzite, flint and quartz. This assemblage is attributed to a Mode 1 technology (Oldowayen), among which macro-tools (hammerstones, shaped and fractured pebbles) are found alongside rarer elements resulting from debitage operating chains aimed at producing sharp-edged flakes, very rarely retouched. The bipolar-on-anvil flaking technique could be identified from the characteristics of some artifacts. Several refitting flakes on shaped pebbles or percussion tools attest to knapping and percussion activities in the cave. Hominins consumed the remains of large herbivore carcasses, as attested by the presence of cutting and fracturing marks on some bones. The presence of a freshwater source in the immediate vicinity, and the knapping and butchering activities here therefore document the subsistence behavior of Lower Pleistocene human groups, certainly in competition with the carnivores present. 相似文献