全文获取类型
收费全文 | 150786篇 |
免费 | 4830篇 |
国内免费 | 13757篇 |
出版年
2022年 | 1216篇 |
2021年 | 3008篇 |
2020年 | 1870篇 |
2019年 | 2740篇 |
2018年 | 2864篇 |
2017年 | 2023篇 |
2016年 | 2709篇 |
2015年 | 4738篇 |
2014年 | 8618篇 |
2013年 | 9239篇 |
2012年 | 7089篇 |
2011年 | 7517篇 |
2010年 | 5658篇 |
2009年 | 6004篇 |
2008年 | 6497篇 |
2007年 | 7276篇 |
2006年 | 6240篇 |
2005年 | 5856篇 |
2004年 | 5271篇 |
2003年 | 4634篇 |
2002年 | 4331篇 |
2001年 | 3718篇 |
2000年 | 3049篇 |
1999年 | 3217篇 |
1998年 | 2883篇 |
1997年 | 2321篇 |
1996年 | 2199篇 |
1995年 | 2316篇 |
1994年 | 2354篇 |
1993年 | 2175篇 |
1992年 | 1907篇 |
1991年 | 1856篇 |
1990年 | 1593篇 |
1989年 | 1448篇 |
1988年 | 1361篇 |
1987年 | 1123篇 |
1986年 | 999篇 |
1985年 | 2623篇 |
1984年 | 3870篇 |
1983年 | 2528篇 |
1982年 | 3058篇 |
1981年 | 2687篇 |
1980年 | 2346篇 |
1979年 | 2181篇 |
1978年 | 1829篇 |
1977年 | 1695篇 |
1976年 | 1528篇 |
1975年 | 1259篇 |
1974年 | 1253篇 |
1973年 | 1214篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
Volatiles from the epicuticular wax of watercress were collected by ether washing and examined using gas chromatographic and mass spectrometric analysi 相似文献
62.
Nabiel A.M. Saleh Zeinab A.R. El-karemy Ragaa M.A. Mansour Abdel-Aziz A. Fayed 《Phytochemistry》1983,22(11):2501-2505
The flavonoids of five Geranium, fourteen Erodium and four Monsonia species were studied. Quercetin was the most common aglycone with lesse 相似文献
63.
Hanna G. Budayeva Arundhati Sengupta-Ghosh Lilian Phu John G. Moffat Gai Ayalon Donald S. Kirkpatrick 《Molecular & cellular proteomics : MCP》2022,21(4):100221
Muscle-specific receptor tyrosine kinase (MuSK) agonist antibodies were developed 2 decades ago to explore the benefits of receptor activation at the neuromuscular junction. Unlike agrin, the endogenous agonist of MuSK, agonist antibodies function independently of its coreceptor low-density lipoprotein receptor–related protein 4 to delay the onset of muscle denervation in mouse models of ALS. Here, we performed dose–response and time-course experiments on myotubes to systematically compare site-specific phosphorylation downstream of each agonist. Remarkably, both agonists elicited similar intracellular responses at known and newly identified MuSK signaling components. Among these was inducible tyrosine phosphorylation of multiple Rab GTPases that was blocked by MuSK inhibition. Importantly, mutation of this site in Rab10 disrupts association with its effector proteins, molecule interacting with CasL 1/3. Together, these data provide in-depth characterization of MuSK signaling, describe two novel MuSK inhibitors, and expose phosphorylation of Rab GTPases downstream of receptor tyrosine kinase activation in myotubes. 相似文献
64.
65.
Feral and laboratory flocks of rock doves () show a pattern of grouped sequential exploitation when simultaneously presented with two dispersed, depleting patches of seed. This behavior contrasts with the ideal free distribution pattern shown when patches are small and concentrated. Grouped sequential exploitation consists of two phases: all pigeons first land together and feed at one patch, then leave one by one for the other patch. Departure times of individuals for the second patch are correlated with feeding rate at patch 1, which is in turn correlated with position in the dominance hierarchy. The decision to switch from patch 1 to patch 2 improves individual feeding rates in all cases, but is done slightly later than it should according to optimal foraging theory. 相似文献
66.
67.
D E Bowman 《Biochemical and biophysical research communications》1979,87(1):78-84
The oxidized B chain of insulin was used as a simple model for further consideration of limited proteolysis with low substrate:enzyme ratios. With low B chain:trypsin ratios, the ordinarily slower cleavage rate of the -Lys29-Ala30 bond essentially equaled the cleavage saturation rate of the -Arg22-Gly23 bond. This led to the disappearance of octapeptide which ordinarily forms most rapidly. Heptapeptide and alanine, formed mainly by cleavage of the octapeptide, decreased somewhat at high enzyme relative levels. Trypsin added to B chain formed a single chromatographic peak. 相似文献
68.
Hiroyoshi Fujita Yutaka Orii Seiyo Sano 《Biochimica et Biophysica Acta (BBA)/General Subjects》1981,678(1):39-50
δ-Aminolevulinic acid dehydratase (porphobilinogen synthase; 5-aminolevulinate hydro-lyase, EC 4.2.1.24) was purified from rat and rabbit erythrocytes to a homogeneous state. Specific activities were 26.0 and 26.6 units/mg protein for the rat and rabbit enzymes, respectively, and their estimated molecular weight was 280 000, each consisting of 8 subunits of Mr 35 000. In order to quantitate rat δ-aminolevulinic acid dehydratase at several stages of lead-poisoning, a radioimmunoassay technique using goat antiserum against the rat enzyme was developed for the first time. This technique was specific, reproducible and high sensitive allowing determination of 1 ng enzyme. When drinking water containing 25 mM lead acetate was given daily to rats ad lib. the δ-aminolevulinic acid dehydratase activity in the blood, assayed without any pretreatment, decreased to 8% of the control level on the next day. On the contrary, the restored enzyme activity, assayed in the presence of Zn2+ and dithiothreitol, was greater than normal by the fourth day of lead administration in bone-marrow cells and by the ninth day in the peripheral blood. The increased activity level stayed the same from the ninth day onward. The enzyme content as determined directly by the radioimmunoassay technique at this stage was about 2-fold above that the control. There was no significant difference in the number of reticulocytes and the distribution profile of different types of reticulocytes between the lead-exposed and non-exposed rats. Therefore, the increase in the amount of δ-aminolevulinic acid dehydratase in erythrocytes of lead-poisoned rats was suggested to be due to an increased rate of synthesis in the bone-marrow cells. 相似文献
69.
Takashi Arakawa Yoshiaki Kamiya 《Biochemical and biophysical research communications》2010,397(2):345-349
We previously reported the identification of DP-1 isoforms (α and β), which are structurally C-terminus-deleted ones, and revealed the low-level expression of these isoforms. It is known that wild-type DP-1 is degraded by the ubiquitin-proteasome system, but few details are known about the domains concerned with the protein stability/instability for the proteolysis of these DP-1 isoforms. Here we identified the domains responsible for the stability/instability of DP-1. Especially, the DP-1 “Stabilon” domain was a C-terminal acidic motif and was quite important for DP-1 stability. Moreover, we propose that this DP-1 Stabilon may be useful for the stability of other nuclear proteins when fused to them. 相似文献
70.
A review of in vitro mutagenesis assessment of metal compounds in mammalian and nonmammalian test systems has been compiled.
Prokaryotic assays are ineffective or inconsistent in their detection of most metals as mutagens, with the notable exception
of hexavalent chromium. Mammalian assay systems appear to be similarly inappropriate for the screening of metal compounds
based upon the limited number of studies that have employed those compounds having known carcinogenic activity. Although of
limited value as screening tests for the detection of potentially carcinogenic metal compounds, the well-characterized in
vitro mutagenesis systems may prove to be of significant value as a means to elucidate mechanisms of metal genotoxicity. 相似文献