全文获取类型
收费全文 | 4706篇 |
免费 | 382篇 |
国内免费 | 2篇 |
专业分类
5090篇 |
出版年
2023年 | 19篇 |
2022年 | 41篇 |
2021年 | 76篇 |
2020年 | 48篇 |
2019年 | 62篇 |
2018年 | 73篇 |
2017年 | 73篇 |
2016年 | 122篇 |
2015年 | 178篇 |
2014年 | 228篇 |
2013年 | 285篇 |
2012年 | 324篇 |
2011年 | 312篇 |
2010年 | 240篇 |
2009年 | 199篇 |
2008年 | 275篇 |
2007年 | 277篇 |
2006年 | 225篇 |
2005年 | 229篇 |
2004年 | 245篇 |
2003年 | 250篇 |
2002年 | 218篇 |
2001年 | 79篇 |
2000年 | 55篇 |
1999年 | 64篇 |
1998年 | 81篇 |
1997年 | 42篇 |
1996年 | 36篇 |
1995年 | 39篇 |
1994年 | 31篇 |
1993年 | 36篇 |
1992年 | 54篇 |
1991年 | 51篇 |
1990年 | 34篇 |
1989年 | 35篇 |
1988年 | 33篇 |
1987年 | 25篇 |
1986年 | 17篇 |
1985年 | 21篇 |
1984年 | 25篇 |
1983年 | 18篇 |
1982年 | 24篇 |
1981年 | 18篇 |
1978年 | 13篇 |
1977年 | 13篇 |
1975年 | 12篇 |
1974年 | 18篇 |
1973年 | 14篇 |
1972年 | 15篇 |
1970年 | 12篇 |
排序方式: 共有5090条查询结果,搜索用时 0 毫秒
11.
Cell and Tissue Research - The infracerebral complex consists of: (a) two types of ependymoid infracerebral cells located on the ventral surface of the brain, adjacent to a coelomic sinus and blood... 相似文献
12.
13.
14.
15.
16.
Thierry Becquer Denis Merlet Jean-Pierre Boudot James Rouiller Francis Gras 《Plant and Soil》1990,125(1):95-107
Nitrate uptake and leaching were measured during one year in a declined fir forest on the Vosges highlands (eastern France),
in order to investigate whether excess nitrification could be responsible for a deleterious acidification of the ecosystem.
Nitrate uptake by the vegetation was active mainly from spring to early fall, and then reached about 66 kg N ha-1. No significant leaching loss occurred during the growth period of the vegetation. Significant nitrate leaching occurred
in winter (about 17 kg N ha-1). During fall and winter the nitrification rate was of the same magnitude as values reported for other ecosystems, and, thus,
was not considered to be abnormaly strong. No abnormal temporal discoupling of nitrate production and nitrate uptake occurred
in the ecosystem, and forest decline must therefore have some other cause. 相似文献
17.
The early component of the postural responses which accompany the limb flexion during unilateral stimulation of the motor cortex in the cat is not of reflex origin, but results from a central command. These postural adjustments are characterized by a decreased force under the limb diagonally opposite to the moving one and an increased force under the other two. Since the lateral vestibular nucleus (LVN) exerts an excitatory influence on ipsilateral limb extensor motoneurons, experiments were performed in cats to establish whether the cortical-induced postural changes were mediated through the LVN. This structure is tonically inhibited by GABAergic synapses originating from Purkinje cells of the cerebellar vermis, so that local microinjection into the LVN of GABA agonists or antagonists should either decrease or increase the spontaneous discharge of their neurons. Unilateral microinjection of 0.25 microliters of the GABA-A agonist muscimol or the GABA-B agonist baclofen (at 2-4 micrograms/microliters saline) into the LVN produced a short-lasting episode of ipsilateral postural hypotonia and contralateral hypertonia, during which the cats were unable to stand on the measurement platform. When, shortly after, some recovery of the postural activity appeared, no changes in threshold, latency or amplitude of the cortical-induced flexion movement were observed; however, the early component of the postural responses decreased in the other three limbs. Moreover, the slope of the response curve of the moving limb remained unmodified, while that of the early component of the postural responses, which involved the remaining limbs, decreased following stimulation of the motor cortex at different stimulus intensities. These effects started a few min after the injection and lasted for about 2-3 h. The effects described above were dose-dependent. Moreover, histological controls indicated that the structure responsible for these postural changes corresponded to the middle part of the LVN. The specificity of the results was shown by the fact that unilateral microinjection of 0.25 microliters of the GABA-A antagonist bicuculline or the GABA-B antagonist phaclofen (at 5-8 micrograms/microliter saline) into the LVN produced a postural asymmetry opposite in sign to that elicited in the same experiments by the corresponding agonists. These injections did not modify the amplitude of the cortical-induced limb flexion, but rather enhanced the amplitude of the early component of the postural responses in the other three limbs.(ABSTRACT TRUNCATED AT 400 WORDS) 相似文献
18.
Genes of theHoxDcomplex related to theDrosophila Abd-Bgene are involved in the morphogenesis of vertebrate paired appendages.Hoxd-11,for instance, is necessary in combination with otherHoxgenes for the proper development of different parts of the tetrapod limbs. Sequence comparisons between the mouse, chicken, and zebrafishHoxd-11loci have revealed the conservation of several blocks of DNA sequence which may be of importance for the regulation ofHoxd-11expression. We have used transgenic mice to show that one of these conserved elements specifically drives expression in a proximal-posterior part of developing forelimbs. Production of mice transgenic for a full fishHoxd-11construct as well as for mouse–fishHoxd-11chimeric constructs shows that the fish counterpart of this sequence is able to elicit expression in mouse forelimbs as well, though in a slightly different domain. However, this fish element requires the presence of the mouse promoter and does not work in its own context. These results are discussed in light of both the control ofHoxdgene expression during limb development and the use of a comparative interspecies approach to understand the regulation of genes involved in vertebrate development. 相似文献
19.
The microbiological fate of polycyclic aromatic hydrocarbons: carbon and oxygen balances for bacterial degradation of model compounds 总被引:3,自引:0,他引:3
M. Bouchez D. Blanchet J. -P. Vandecasteele 《Applied microbiology and biotechnology》1996,45(4):556-561
A series of pure bacterial strains belonging mainly to theRhodococcus andPseudomonas genera were grown on one of the following polycyclic aromatic hydrocarbons (PAH) supplied as sole carbon and energy source: naphthalene, fluorene, phenanthrene, anthracene, fluoranthene and pyrene. In each case, a quantitative evaluation of the carbon repartition of the PAH degraded into CO2, biomass and water-soluble metabolites was carried out. In addition, the kinetics of oxygen consumption and of water-soluble metabolite accumulation during PAH biodegradation was followed with respirometric equipment. Satisfactory carbon balances were obtained and the data correlated well with oxygen consumption values. The results show that growth on PAH presents high mineralization yields (from 56% to 77% of carbon) and sizeable production of biomass (from 16% to 35% of carbon) and limited but significant accumulation of metabolites (from 5% to 23% of carbon). The mineralization yields were higher and biomass yields lower in the case of higher PAH. Some differences between strains were also observed. 相似文献
20.