全文获取类型
收费全文 | 8439篇 |
免费 | 614篇 |
国内免费 | 5篇 |
专业分类
9058篇 |
出版年
2023年 | 43篇 |
2022年 | 93篇 |
2021年 | 195篇 |
2020年 | 130篇 |
2019年 | 123篇 |
2018年 | 181篇 |
2017年 | 149篇 |
2016年 | 281篇 |
2015年 | 401篇 |
2014年 | 461篇 |
2013年 | 570篇 |
2012年 | 693篇 |
2011年 | 712篇 |
2010年 | 439篇 |
2009年 | 379篇 |
2008年 | 495篇 |
2007年 | 515篇 |
2006年 | 504篇 |
2005年 | 417篇 |
2004年 | 382篇 |
2003年 | 302篇 |
2002年 | 333篇 |
2001年 | 77篇 |
2000年 | 55篇 |
1999年 | 58篇 |
1998年 | 89篇 |
1997年 | 36篇 |
1996年 | 51篇 |
1995年 | 52篇 |
1994年 | 49篇 |
1993年 | 48篇 |
1992年 | 40篇 |
1991年 | 40篇 |
1990年 | 32篇 |
1989年 | 36篇 |
1988年 | 33篇 |
1987年 | 43篇 |
1986年 | 29篇 |
1985年 | 39篇 |
1984年 | 36篇 |
1983年 | 46篇 |
1982年 | 34篇 |
1981年 | 35篇 |
1980年 | 23篇 |
1979年 | 23篇 |
1978年 | 19篇 |
1977年 | 34篇 |
1976年 | 20篇 |
1973年 | 14篇 |
1964年 | 14篇 |
排序方式: 共有9058条查询结果,搜索用时 0 毫秒
51.
Callus was induced from mature leaf lamina, petiole, stem, and main and branch root of Panax ginseng and maintained under different nutrient and light conditions. Heterogenous callus cultures differentiated organoids and/or embryoids. Embryoids that arose from callus cultures of leaf origin germinated into shoots. The occurrence of the early stages of different regenerated structures was proved on histological level. 相似文献
52.
A new homeobox-leucine zipper gene from Arabidopsis thaliana 总被引:3,自引:0,他引:3
Jim Mattsson Eva Söderman Marie Svenson Chumpol Borkird Peter Engström 《Plant molecular biology》1992,18(5):1019-1022
We have isolated a homeobox-containing gene from Arabidopsis thaliana using a degenerate oligonucleotide probe corresponding to the most conserved region of the homeodomain. This strategy has been used previously to isolate homeobox-containing genes from Caenorhabditis, and recently from A. thaliana. The Arabidopsis genes have an unusual structure in that they have a leucine zipper motif adjacent to the carboxy terminal region of the homeo domain, a feature not found in homeobox-containing genes isolated from animals. We report the isolation and primary structure of a new member of this Arabidopsis homeobox-leucine zipper gene family. This new member has the homeodomain and leucine-zipper motif similar to the two genes previously identified, but differs from these genes in the part corresponding to the carboxy terminus of the polypeptide, as well as in size and isoelectric point of the protein. 相似文献
53.
Summary T-cell cultures derived from the blood of 14 patients with solid tumors were propagated with T-cell growth factor (TCGF). The cultures were initiated from lymphocytes exposed to autologous tumor-biopsy cells. TCGF was added either immediately or 3–10 days later. In the former culture type the cell yield on day 7 was considerably higher. The cytotoxic potential of the cultured cells was assayed on two occasions, between days 7 and 10 and between weeks 5 and 8. Cells of all but two cultures had the potential to lyse autologous tumor-biopsy cells.On the population level, cytotoxicity was specific for autologous tumor in those cultures that were driven to growth with TCGF after the 3rd day. These lymphocytes did not lyse allogeneic tumor-biopsy cells. In contrast, all five cultures initiated in the presence of TCGF exhibited a broader cytotoxic potential, i.e., in addition to the stimulator autologous-tumor cells, they also lysed other targets. Another difference between the two culture types was their behavior toward K562. Tested on the 7th day they all lysed K562; however, this function declined in strength or disappeared later in the cultures exposed to TCGF after the 3rd day.Reexposure of the lymphocytes to autologous tumor-biopsy cells after 2 weeks of culture period, but not on the 7th day, induced DNA synthesis. This secondary response was specific inasmuch as allogeneic tumor cells had little or no effect.One of the autotumor restimulated cultures was tested for cytotoxic potential. It increased against the autologous but not against other tumors or K562 cells. 相似文献
54.
Lawrence L. Johnson Evelyn L. Sargent Linda L. Washburn Eva M. Eicher 《Genesis (New York, N.Y. : 2000)》1982,3(3):247-253
Karyotypically XY individuals of the C57BL/6J-YPOS mouse stock develop as females or hermaphrodites, but never as normal males. The aberrant sexual development results from the interaction of the C57BL/6J genetic background with the M. poschiavinus-derived Y chromosome. XY females from this stock were assayed for H-Y antigen. By the criteria of skin-grafting, the cell-mediated lympholysis test, and the popliteal lymph node assay, these XY females are antigenically indistinguishable from normal C57BL/6 males. Implications for the hypothesis that H-Y antigen induces formation of the mammalian testis are discussed. 相似文献
55.
H-2 loss variant sublines of a sarcoma (M-AS), induced by methylcholanthrene in an (A × A.SW)F1 mouse, were used to study the role of the MHC products in the recognition of MC-TSTA. The two reciprocal variant sublines (M-A and M-S) were found to express the TSTA of the original tumor as shown by cross-reactions in graft rejection experiments performed in (A × A.SW)F1 mice. In the A/Sn and A.SW mice the presence of the reciprocal parental H-2 antigens on the immunizing cells decreased the response against the tumor antigens. An admixture of lymphocytes derived from hyperimmune mice inhibited the outgrowth of the tumor cells. The growth inhibition was mediated by T cells and was H-2 restricted. Cells derived from hyperimmune syngeneic mice inhibited the outgrowth of the variant subline used for immunization but had no effect on the reciprocal variant subline. 相似文献
56.
Summary The majority of lymphocytes separated from tumor cell suspensions were T cells. Conjugates of T lymphocytes and tumor cells were often seen. Variable numbers of T cells exhibited signs of activation such as the ability to form stable E rosettes and attachment to normal and malignant cells (a phenomenon designated natural attachment: NA). A proportion of T cells activated in vitro by allogeneic stimulation regularly exhibit these properties. The T cell-tumor conjugates in the suspensions may represent the NA phenomenon, but they could also be the product of T cells that adhere on the basis of specific recognition of cell surface antigens.Abbreviations BBS
balanced salt solution
- E rosettes
rosettes formed with sheep erythrocytes
- EA rosettes
rosettes formed with ox erythrocytes coated with anti-ox IgG
- FCS
fetal calf serum
- MLC
mixed lymphocyte cultures
- NA
natural attachment
- PBL
peripheral blood lymphocytes
- SRBC
sheep erythrocytes
- T lymphocytes
thymusderived lymphocytes 相似文献
57.
Synchronous beating between chick embryonic heart cell aggregates and heart cell layers was used to study the relationship between intercellular adhesion and ionic coupling. Adhesion was measured by counting the proportion of aggregates which were not to be removed from cell layers by gentle washing after a 30 min incubation. Synchrony between bound aggregates and contiguous layers was assessed by phase microscopy. The first evidence of synchrony was seen 1.5 h after addition of aggregates to layers, following which there was an increase in the percentage of aggregates beating synchronously, reaching over 50% at 7 h and slowly increasing to a maximum of 65% by 24 h. Scanning electron microscopy and autoradiography of thymidine-labeled cells suggest that synchrony does not depend on cell movement at the interface between aggregate and layer. Acquisition of synchrony can be prevented completely by inhibiting protein synthesis, although pulsation of aggregates and layers continues in proportions unchanged from controls. After reversal of protein synthesis inhibition, synchrony is acquired at a rate and to an extent closely resembling that of newly adherent controls. These data indicate that ionic coupling is neither an inevitable nor an immediate consequence of adhesion. Since ionic coupling has been shown to correlate with the presence of gap junctions, the findings suggest that gap junctions are not involved in the initial events responsible for intercellular adhesion in vitro and that their formation following adhesion in this system may depend upon protein synthesis. 相似文献
58.
Eva M. Håkansson 《Biochemical genetics》1976,14(9-10):869-875
Kidney β-glucuronidase activity in C57BL/Kl and DBA/2/Kl male mice differs about tenfold, C57 giving low and DBA high values. Another C57 subline, C57BL/6J, has slightly higher activity than C57BL/Kl. There is an association between the kidney glucuronidase activity and coat color determined by the buff locus, which indicates that part of the variation is due to differences at the Gur locus. The bf allele per se raises the activity of the enzyme. The backcross distributions give evidence that at least one more locus is involved. 相似文献
59.
60.