全文获取类型
收费全文 | 52149篇 |
免费 | 4264篇 |
国内免费 | 2738篇 |
出版年
2023年 | 490篇 |
2022年 | 537篇 |
2021年 | 2145篇 |
2020年 | 1432篇 |
2019年 | 1745篇 |
2018年 | 1711篇 |
2017年 | 1336篇 |
2016年 | 1955篇 |
2015年 | 2954篇 |
2014年 | 3419篇 |
2013年 | 3797篇 |
2012年 | 4391篇 |
2011年 | 4155篇 |
2010年 | 2415篇 |
2009年 | 2160篇 |
2008年 | 2641篇 |
2007年 | 2410篇 |
2006年 | 2104篇 |
2005年 | 1884篇 |
2004年 | 1613篇 |
2003年 | 1478篇 |
2002年 | 1262篇 |
2001年 | 1171篇 |
2000年 | 1059篇 |
1999年 | 989篇 |
1998年 | 549篇 |
1997年 | 553篇 |
1996年 | 497篇 |
1995年 | 445篇 |
1994年 | 461篇 |
1993年 | 367篇 |
1992年 | 602篇 |
1991年 | 529篇 |
1990年 | 460篇 |
1989年 | 397篇 |
1988年 | 355篇 |
1987年 | 307篇 |
1986年 | 246篇 |
1985年 | 283篇 |
1984年 | 187篇 |
1983年 | 177篇 |
1982年 | 125篇 |
1981年 | 96篇 |
1980年 | 89篇 |
1979年 | 124篇 |
1978年 | 96篇 |
1977年 | 121篇 |
1976年 | 95篇 |
1974年 | 87篇 |
1973年 | 89篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
Yi-Hua Wu Chia-Pei Chang Chin-I Chien Yi-Kuan Tseng Chien-Chia Wang 《Molecular and cellular biology》2013,33(17):3515-3523
The yeast Saccharomyces cerevisiae possesses two distinct glycyl-tRNA synthetase (GlyRS) genes: GRS1 and GRS2. GRS1 is dually functional, encoding both cytoplasmic and mitochondrial activities, while GRS2 is dysfunctional and not required for growth. The protein products of these two genes, GlyRS1 and GlyRS2, are much alike but are distinguished by an insertion peptide of GlyRS1, which is absent from GlyRS2 and other eukaryotic homologues. We show that deletion or mutation of the insertion peptide modestly impaired the enzyme''s catalytic efficiency in vitro (with a 2- to 3-fold increase in Km and a 5- to 8-fold decrease in kcat). Consistently, GRS2 can be conveniently converted to a functional gene via codon optimization, and the insertion peptide is dispensable for protein stability and the rescue activity of GRS1 at 30°C in vivo. A phylogenetic analysis further showed that GRS1 and GRS2 are paralogues that arose from a gene duplication event relatively recently, with GRS1 being the predecessor. These results indicate that GlyRS2 is an active enzyme essentially resembling the insertion peptide-deleted form of GlyRS1. Our study suggests that the insertion peptide represents a novel auxiliary domain, which facilitates both productive docking and catalysis of cognate tRNAs. 相似文献
2.
3.
4.
U Mura A M Osman A S Mohamed D Di Martino P L Ipata 《Comparative biochemistry and physiology. B, Comparative biochemistry》1987,87(1):157-160
The preservation of purine ring as purine bases appears to be a common feature of camel liver. Hepatic guanine appears to be actively converted into GMP in the camel rather than further degraded. The limiting step of guanine degradation appears to be the lack of hepatic guanase activity. Higher purine bases over uric acid ratios were found in camel urine with respect to those of zebu. 相似文献
5.
6.
7.
8.
Lucia Di Giambattista P. Grimaldi S. Gaudenzi D. Pozzi M. Grandi S. Morrone I. Silvestri A. Congiu Castellano 《European biophysics journal : EBJ》2010,39(6):929-934
We have made a preliminary analysis of the results about the effects on tumoral cell line (lymphoid T cell line Jurkat) induced
by UVB radiation (dose of 310 mJ/cm2) with and without a vegetable mixture. In the present study, we have used two techniques: Fourier transform infrared spectroscopy
(FTIR) and flow cytometry. FTIR spectroscopy has the potential to provide the identification of the vibrational modes of some
of the major compounds (lipid, proteins and nucleic acids) without being invasive in the biomaterials. The second technique
has allowed us to perform measurements of cytotoxicity and to assess the percentage of apoptosis. We already studied the induction
of apoptotic process in the same cell line by UVB radiation; in particular, we looked for correspondences and correlations
between FTIR spetroscopy and flow cytometry data finding three highly probable spectroscopic markers of apoptosis (Pozzi et
al. in Radiat Res 168:698–705, 2007). In the present work, the results have shown significant changes in the absorbance and
spectral pattern in the wavenumber protein and nucleic acids regions after the treatments. 相似文献
9.
The neuropeptide thyrotropin releasing hormone (TRH) is capable of influencing both neuronal mechanisms in the brain and the activity of the pituitary-thyroid endocrine axis. By the use of immunocytochemical techniques, first the ultrastructural features of TRH-immunoreactive (IR) perikarya and neuronal processes were studied, and then the relationship between TRH-IR neuronal elements and dopamine-beta-hydroxylase (DBH) or phenylethanolamine-N-methyltransferase (PNMT)-IR catecholaminergic axons was analyzed in the parvocellular subnuclei of the hypothalamic paraventricular nucleus (PVN). In control animals, only TRH-IR axons were detected and some of them seemed to follow the contour of immunonegative neurons. Colchicine treatment resulted in the appearance of TRH-IR material in parvocellular neurons of the PVN. At the ultrastructural level, immunolabel was associated with rough endoplasmic reticulum, free ribosomes and neurosecretory granules. Non-labelled axons formed synaptic specializations with both dendrites and perikarya of the TRH-synthesizing neurons. TRH-IR axons located in the parvocellular units of the PVN exhibited numerous intensely labelled dense-core and fewer small electron lucent vesicles. These axons were frequently observed to terminate on parvocellular neurons, forming both bouton- and en passant-type connections. The simultaneous light microscopic localization of DBH or PNMT-IR axons and TRH-synthesizing neurons demonstrated that catecholaminergic fibers established contacts with the dendrites and cell bodies of TRH-IR neurons. Ultrastructural analysis revealed the formation of asymmetric axo-somatic and axo-dendritic synaptic specializations between PNMT-immunopositive, adrenergic axons and TRH-IR neurons in the periventricular and medial parvocellular subnuclei of the PVN. These morphological data indicate that the hypophysiotrophic, thyrotropin releasing hormone synthesizing neurons of the PVN are directly influenced by the central epinephrine system and that TRH may act as a neurotransmitter or neuromodulator upon other paraventricular neurons. 相似文献
10.