全文获取类型
收费全文 | 13368篇 |
免费 | 1234篇 |
国内免费 | 1853篇 |
出版年
2024年 | 51篇 |
2023年 | 233篇 |
2022年 | 547篇 |
2021年 | 782篇 |
2020年 | 579篇 |
2019年 | 655篇 |
2018年 | 643篇 |
2017年 | 491篇 |
2016年 | 630篇 |
2015年 | 986篇 |
2014年 | 1033篇 |
2013年 | 1167篇 |
2012年 | 1344篇 |
2011年 | 1213篇 |
2010年 | 682篇 |
2009年 | 688篇 |
2008年 | 716篇 |
2007年 | 628篇 |
2006年 | 601篇 |
2005年 | 498篇 |
2004年 | 366篇 |
2003年 | 291篇 |
2002年 | 260篇 |
2001年 | 157篇 |
2000年 | 160篇 |
1999年 | 157篇 |
1998年 | 102篇 |
1997年 | 96篇 |
1996年 | 74篇 |
1995年 | 72篇 |
1994年 | 67篇 |
1993年 | 48篇 |
1992年 | 79篇 |
1991年 | 53篇 |
1990年 | 46篇 |
1989年 | 36篇 |
1988年 | 30篇 |
1987年 | 31篇 |
1986年 | 26篇 |
1985年 | 27篇 |
1984年 | 13篇 |
1983年 | 12篇 |
1982年 | 13篇 |
1981年 | 6篇 |
1978年 | 8篇 |
1977年 | 5篇 |
1973年 | 5篇 |
1972年 | 4篇 |
1971年 | 6篇 |
1970年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
西双版纳傣族“龙山”的生态学意义 总被引:25,自引:3,他引:22
傣族“龙山”是西双版纳地区傣族的民族植物文化中的一例。其概念是“神居住的地方”,在这个地方的动植物都是神的家园里的生灵,是神的伴侣,是不能砍伐、狩猎和破坏的。人 相似文献
32.
小竹鼠在我国仅分布于云南西部热带亚热带地区。主要生活于山坡稀树灌丛、阔叶林、橡胶园及居民点附近。在盈江县分布于海拔300-950米地带。取食、休息、繁殖主要在洞道内。洞系由洞口、取食道、趋避道、窝及“厕所”组成。食物主要有棕叶芦、芦竹及三叶橡胶等18种,尤喜食橡胶树主根,因而对橡胶树危害很大。13号标本中雌7雄6。在盈江每胎2-3只,以2只为多。成年小竹鼠过独居生活,雌雄各有自己的洞系。 相似文献
33.
The sulfhydryl-specific, heterobifunctional, photoactivatable cross-linker 4-maleimidobenzophenone (BPMal) was used to study the interaction of rabbit skeletal muscle troponin subunits TnC, TnT, and TnI. TnC was labeled at Cys-98 by the maleimide moiety of BPMal and then mixed with either TnT alone or TnI plus TnT, in the presence of Ca2+. Upon photolysis, TnI and/or TnT formed covalent cross-links with TnC. The cross-linked TnC-TnT heterodimer obtained from the binary complex was digested into progressively smaller cross-linked peptides that were purified by HPLC and then characterized by amino acid analysis and sequencing. An initial cross-linked CNBr fraction contained the expected peptide CB9 (residues 84-135) of TnC, plus CNBr peptides spanning residues 152-230 of TnT. Results from a peptic digest of the CNBr cross-linked fraction permitted the identification of residues 159-197 as the most highly cross-linked region in TnT. A final subtilisin digest yielded a heterogeneous cross-linked fraction, which suggested that an especially high degree of cross-links was formed in the vicinity of residues 175-178 (Met-Lys-Lys-Lys) of TnT. Although this region of TnT had previously been implicated in binding, we show here for the first time that it is close to Cys-98 of TnC. In an analogous study on the binary complex of TnC and TnI [Leszyk, J., Collins, J. H., Leavis, P. C., & Tao, T. (1987) Biochemistry 26, 7042-7047], we previously showed that Cys-98 of TnC was cross-linked mainly to CN4, the "inhibitory region", of TnI.(ABSTRACT TRUNCATED AT 250 WORDS) 相似文献
34.
The ability to serially propagate mammalian cells in microcarrier cultures is essential for large-scale operation. The success of such serial propagation depends on viable dissociation of cells from microcarriers and the normal growth and product formation after subsequent reinoculation. The high pH treatment developed for dissociating cells from DEAE-derivatized microcarriers was not as effective for a number of cell strains cultivated on gelatin-coated microcarriers. By prewashing the cell-laden microcarriers with buffer containing a chelating agent, bovine kidney cells, BK, human embryonic foreskin fibroblasts, FS-4, and continuous human kidney cells, TCL-598 which produces prourokinase, were viably dissociated from commercially available gelatin-coated microcarriers, Cytodex-3. Cells dissociated from microcarriers reattached and grew on micro-carriers subsequent to inoculation into subcultures. However, after subculturing, cells may attach at different rates to newly added beads and to conditioned microcarriers which cells had previously grown. It resulted in an uneven cell distribution on microcarriers and inferior growth kinetics. This effect was more profound for BK and FS-4 cells which are propagated with a low multiplication ratio. Specifically, BK cells attach to conditioned beads at a faster rate than to new beads, while FS-4 cells attach to new beads faster than to conditioned beads. Thus, for these two cell strains, a separator was used to separate the microcarriers from the suspension of dissociated cells before subsequent inoculation. For TCL-598 cells, which are propagated at a high multiplication ratio, this dissociation technique can be applied directly without the separation of dissociated cells and conditioned microcarriers. All the three cell lines tested exhibit normal growth kinetics in serial propagation on microcarriers. Furthermore, the production of prourokinase by TCL598 cells serially propagated on microcarriers was comparable to that inoculated from roller bottles. 相似文献
35.
The effects of phosphorylation on the interaction between spectrin and ankyrin were investigated. Spectrin and ankyrin were phosphorylated using purified human erythrocyte membrane and cytosolic (casein kinase A) kinases. These two kinases have similar properties as well as activities toward spectrin and ankyrin. Both kinases catalyzed the incorporation of about 2 mol of phosphate/mol of spectrin and about 7 mol of phosphate/mol of ankyrin. These phosphates were incorporated primarily into seryl and threonyl residues of the proteins. The phosphopeptide maps of ankyrin phosphorylated by the membrane kinase and casein kinase A were identical. Binding studies indicate that ankyrin exhibits different affinities for spectrin dimers (KD = 2.5 +/- 0.9 X 10(-6) M) and tetramers (KD = 2.7 +/- 0.8 X 10(-7) M). These dissociation constants were not appreciably affected by the phosphorylation of spectrin. On the other hand, phosphorylation of ankyrin was found to significantly reduce its affinity for either phosphorylated or unphosphorylated spectrin tetramers (KD = 1.2 +/- 0.1 X 10(-6) M) but not spectrin dimers (KD = 2.5 +/- 0.4 X 10(-6) M). The same results were obtained using either the membrane kinase or casein kinase A as the phosphorylating enzyme. The above observation suggests that ankyrin phosphorylation may provide an important mechanism for the regulation of the erythrocyte membrane cytoskeletal network. 相似文献
36.
元江干热河谷山地五百年来植被变迁探讨 总被引:15,自引:2,他引:13
元江河谷是云南省最干热地区之一,在海拔800—900米以下的山地上广泛分布着稀树灌草丛。根据《元江府志》(1714年编纂)、《元江州志》(1826年编纂)、《元江志稿》(1922年编篡)及对现存植被的考察,本文探讨了元江干热河谷山地五百年来植被的变迁。 元江县森林复盖率的减少与人口的增加有密切关系,十七世纪中期以前,森林复盖率在75%以上,十八、十九世纪时为70%左右,1958年为61.5%,1975年为27.3%,至1982年则为19.3%。研究表明,在十九世纪以前,这个地区分布的主要植被是热带季雨林,甚而热带季节雨林,以后热带稀树灌草丛则迅速发展。植被的历史变化与土壤流失密切相关。植物群落的演变是由以乔木树种为优势演变为以灌木种类为优势,再演变为以多年生草木植物为优势,而最后则成为裸地。本文也讨论了这个地区植被恢复的方法。 相似文献
37.
从3例急性成人腹泻患者粪便中,经电镜观察,成人腹泻轮状病毒—酶联免疫吸附试验(ADRV-ELISA)、普通轮状病毒—酶联免疫吸附试验(Rota-ELISA),猪抗C型(组)轮状病毒和鸡抗D型(组)轮状病毒血清分别与本病毒的免疫电镜试验以及RNA电泳等实验结果,发现了一种新轮状病毒,该病毒的形态结构与普通轮状病毒(Rotavirus)、成人腹泻论状病毒(Adult Diarrhoea Rotavirus,简称ADRV)极为相似,但抗原性与普通轮状病毒(A组),成人腹泻轮状病毒(B组),C型轮状病毒(C组),D型轮状病毒(D组)显然无关。基因分析表明,该病毒基因组由11个双链RNA片段组成,但其RNA电泳图型具有独自的特点,与目前公认的A组、B组、C组、D组论状病毒韵RNA电泳图型均不同,免疫电镜证实,该病毒能被人恢复期血清所凝集,表明该病毒可能是腹泻病人的病因。 相似文献
38.
39.
Effects of camptothecin, a naturally occurring alkaloid, on seed germination varied from promotive to inhibitory, depending on the species used. It markedly inhibited seedling root growth but its inhibition of hypocotyl growth varied among species. Camptothecin inhibited GA3-induced dark germination of lettuce (Lactuca sativa L.) seeds and hypocotyl elongation of seedlings. In contrast to ABA, the camptothecin inhibition of GA3-induced germination could not be overcome by cytokinin. When seeds were germinated at 29C with a 0.5 h light treatment, little or no germination occurred in the camptothecin treatment, but addition of cytokinin overcame this inhibition. 相似文献
40.