全文获取类型
收费全文 | 3953篇 |
免费 | 91篇 |
国内免费 | 21篇 |
专业分类
系统科学 | 136篇 |
丛书文集 | 4篇 |
教育与普及 | 3篇 |
理论与方法论 | 34篇 |
现状及发展 | 1107篇 |
研究方法 | 178篇 |
综合类 | 2546篇 |
自然研究 | 57篇 |
出版年
2024年 | 14篇 |
2023年 | 27篇 |
2020年 | 15篇 |
2018年 | 13篇 |
2017年 | 21篇 |
2016年 | 35篇 |
2015年 | 65篇 |
2014年 | 40篇 |
2013年 | 30篇 |
2012年 | 240篇 |
2011年 | 303篇 |
2010年 | 39篇 |
2008年 | 83篇 |
2007年 | 87篇 |
2006年 | 68篇 |
2005年 | 262篇 |
2004年 | 555篇 |
2003年 | 505篇 |
2002年 | 186篇 |
2001年 | 76篇 |
2000年 | 142篇 |
1999年 | 75篇 |
1992年 | 37篇 |
1991年 | 25篇 |
1990年 | 35篇 |
1989年 | 36篇 |
1988年 | 34篇 |
1987年 | 19篇 |
1986年 | 31篇 |
1985年 | 36篇 |
1984年 | 26篇 |
1983年 | 26篇 |
1982年 | 18篇 |
1980年 | 18篇 |
1979年 | 67篇 |
1978年 | 43篇 |
1977年 | 32篇 |
1976年 | 30篇 |
1975年 | 38篇 |
1974年 | 60篇 |
1973年 | 53篇 |
1972年 | 52篇 |
1971年 | 66篇 |
1970年 | 59篇 |
1969年 | 70篇 |
1968年 | 59篇 |
1967年 | 43篇 |
1966年 | 56篇 |
1965年 | 41篇 |
1964年 | 11篇 |
排序方式: 共有4065条查询结果,搜索用时 46 毫秒
141.
The apicomplexan plastid and its evolution 总被引:1,自引:0,他引:1
Sato S 《Cellular and molecular life sciences : CMLS》2011,68(8):1285-1296
Protistan species belonging to the phylum Apicomplexa have a non-photosynthetic secondary plastid—the apicoplast. Although
its tiny genome and even the entire nuclear genome has been sequenced for several organisms bearing the organelle, the reason
for its existence remains largely obscure. Some of the functions of the apicoplast, including housekeeping ones, are significantly
different from those of other plastids, possibly due to the organelle’s unique symbiotic origin. 相似文献
142.
Translation initiation is a critical step in protein synthesis. Previously, two major mechanisms of initiation were considered
as essential: prokaryotic, based on SD interaction; and eukaryotic, requiring cap structure and ribosomal scanning. Although
discovered decades ago, cap-independent translation has recently been acknowledged as a widely spread mechanism in viruses,
which may take place in some cellular mRNA translations. Moreover, it has become evident that translation can be initiated
on the leaderless mRNA in all three domains of life. New findings demonstrate that other distinguishable types of initiation
exist, including SD-independent in Bacteria and Archaea, and various modifications of 5′ end-dependent and internal initiation
mechanisms in Eukarya. Since translation initiation has developed through the loss, acquisition, and modification of functional
elements, all of which have been elevated by competition with viral translation in a large number of organisms of different
complexity, more variation in initiation mechanisms can be anticipated. 相似文献
143.
Windus LC Chehrehasa F Lineburg KE Claxton C Mackay-Sim A Key B St John JA 《Cellular and molecular life sciences : CMLS》2011,68(19):3233-3247
Axons of primary olfactory neurons are intimately associated with olfactory ensheathing cells (OECs) from the olfactory epithelium until the final targeting of axons within the olfactory bulb. However, little is understood about the nature and role of interactions between OECs and axons during development of the olfactory nerve pathway. We have used high resolution time-lapse microscopy to examine the growth and interactions of olfactory axons and OECs in vitro. Transgenic mice expressing fluorescent reporters in primary olfactory axons (OMP-ZsGreen) and ensheathing cells (S100ß-DsRed) enabled us to selectively analyse these cell types in explants of olfactory epithelium. We reveal here that rather than providing only a permissive substrate for axon growth, OECs play an active role in modulating the growth of pioneer olfactory axons. We show that the interactions between OECs and axons were dependent on lamellipodial waves on the shaft of OEC processes. The motility of OECs was mediated by GDNF, which stimulated cell migration and increased the apparent motility of the axons, whereas loss of OECs via laser ablation of the cells inhibited olfactory axon outgrowth. These results demonstrate that the migration of OECs strongly regulates the motility of axons and that stimulation of OEC motility enhances axon extension and growth cone activity. 相似文献
144.
Root nodule (RN) symbiosis has a unique feature in which symbiotic bacteria fix atmospheric nitrogen. The symbiosis is established
with a limited species of land plants, including legumes. How RN symbiosis evolved is still a mystery, but recent findings
on legumes genes that are necessary for RN symbiosis may give us a clue. 相似文献
145.
146.
Amiot L Ferrone S Grosse-Wilde H Seliger B 《Cellular and molecular life sciences : CMLS》2011,68(3):417-431
Although the expression of the non-classical HLA class I molecule HLA-G was first reported to be restricted to the fetal–maternal
interface on the extravillous cytotrophoblasts, the distribution of HLA-G in normal tissues appears broader than originally
described. HLA-G expression was found in embryonic tissues, in adult immune privileged organs, and in cells of the hematopoietic
lineage. More interestingly, under pathophysiological conditions HLA-G antigens may be expressed on various types of malignant
cells suggesting that HLA-G antigen expression is one strategy used by tumor cells to escape immune surveillance. In this
article, we will focus on HLA-G expression in cancers of distinct histology and its association with the clinical course of
diseases, on the underlying molecular mechanisms of impaired HLA-G expression, on the immune tolerant function of HLA-G in
tumors, and on the use of membrane-bound and soluble HLA-G as a diagnostic or prognostic biomarker to identify tumors and
to monitor disease stage, as well as on the use of HLA-G as a novel therapeutic target in cancer. 相似文献
147.
148.
In 1905, Albert Einstein proposed that the forces that cause the random Brownian motion of a particle also underlie the resistance
to macroscopic motion when a force is applied. This insight, of a coupling between fluctuation (stochastic behavior) and responsiveness
(non-stochastic behavior), founded an important branch of physics. Here we argue that his insight may also be relevant for
understanding evolved biological systems, and we present a ‘fluctuation–response relationship’ for biology. The relationship
is consistent with the idea that biological systems are similarly canalized to stochastic, environmental, and genetic perturbations.
It is also supported by in silico evolution experiments, and by the observation that ‘noisy’ gene expression is often both
more responsive and more ‘evolvable’. More generally, we argue that in biology there is (and always has been) an important
role for macroscopic theory that considers the general behavior of systems without concern for their intimate molecular details. 相似文献
149.
Hosseinkhani S 《Cellular and molecular life sciences : CMLS》2011,68(7):1167-1182
Firefly luciferase-catalyzed reaction proceeds via the initial formation of an enzyme-bound luciferyl adenylate intermediate.
The chemical origin of the color modulation in firefly bioluminescence has not been understood until recently. The presence
of the same luciferin molecule, in combination with various mutated forms of luciferase, can emit light at slightly different
wavelengths, ranging from red to yellow to green. A historical perspective of development in understanding of color emission
mechanism is presented. To explain the variation in the color of the bioluminescence, different factors have been discussed
and five hypotheses proposed for firefly bioluminescence color. On the basis of recent results, light-color modulation mechanism
of firefly luciferase propose that the light emitter is the excited singlet state of OL− [1(OL−)*], and light emission from 1(OL−)* is modulated by the polarity of the active-site environment at the phenol/phenolate terminal of the benzothiazole fragment
in oxyluciferin. 相似文献
150.