全文获取类型
收费全文 | 32078篇 |
免费 | 1643篇 |
国内免费 | 44篇 |
专业分类
33765篇 |
出版年
2023年 | 236篇 |
2022年 | 579篇 |
2021年 | 1022篇 |
2020年 | 586篇 |
2019年 | 620篇 |
2018年 | 943篇 |
2017年 | 920篇 |
2016年 | 1149篇 |
2015年 | 1415篇 |
2014年 | 1693篇 |
2013年 | 2350篇 |
2012年 | 2500篇 |
2011年 | 2311篇 |
2010年 | 1342篇 |
2009年 | 1218篇 |
2008年 | 1404篇 |
2007年 | 1389篇 |
2006年 | 1168篇 |
2005年 | 1039篇 |
2004年 | 927篇 |
2003年 | 774篇 |
2002年 | 696篇 |
2001年 | 619篇 |
2000年 | 568篇 |
1999年 | 487篇 |
1998年 | 215篇 |
1997年 | 178篇 |
1996年 | 178篇 |
1995年 | 187篇 |
1994年 | 157篇 |
1993年 | 150篇 |
1992年 | 366篇 |
1991年 | 338篇 |
1990年 | 307篇 |
1989年 | 272篇 |
1988年 | 285篇 |
1987年 | 251篇 |
1986年 | 224篇 |
1985年 | 254篇 |
1984年 | 244篇 |
1983年 | 159篇 |
1982年 | 150篇 |
1981年 | 146篇 |
1980年 | 133篇 |
1979年 | 201篇 |
1978年 | 143篇 |
1977年 | 135篇 |
1974年 | 146篇 |
1973年 | 119篇 |
1972年 | 126篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
251.
Detection of a homologous series of C26-C38 polyenoic fatty acids in the brain of patients without peroxisomes (Zellweger''s syndrome). 总被引:2,自引:1,他引:1
下载免费PDF全文
![点击此处可从《The Biochemical journal》网站下载免费的PDF全文](/ch/ext_images/free.gif)
A Poulos P Sharp H Singh D Johnson A Fellenberg A Pollard 《The Biochemical journal》1986,235(2):607-610
The brains of patients with inherited abnormalities in peroxisomal structure and function contain greatly increased proportions of a homologous series of unique polyenoic fatty acids with carbon chain lengths ranging from 26 to 38. Based on evidence by chemical ionization and electron impact mass spectrometry before and after catalytic hydrogenation, and argentation t.l.c., these lipids have been tentatively identified as 26:5, 28:5, 30:5, 30:6, 30:7, 32:5, 32:6, 32:7, 34:5 and 34:6 fatty acids. A further two fatty acids eluting at very high temperatures from gas chromatography columns have been tentatively identified on the basis of their chemical ionization mass spectra as 36:6 and 38:6 fatty acids. 相似文献
252.
Amit Kumar Jana Sanjiv Agarwal S. N. Chatterjee 《Radiation and environmental biophysics》1986,25(4):309-314
Summary Ultrasonic radiation produced a dose dependent linear increase in lipid peroxidation (MDA formation) in the liposomal membrane. The yield of MDA was significantly inhibited by butylated hydroxytoluene (BHT), the antioxidant, sodium formate, the OH radical scavenger, and EDTA, the metal ion chelator. Ascorbic acid at low concentration increased the ultrasonic induced MDA formation while high concentrations inhibited lipid peroxidation. A mechanism of ultrasound induced lipid peroxidation is suggested. 相似文献
253.
Micrococcal nuclease was used as a probe to study chromatin structure in control and ataxia-telangiectasia cells. The rate and extent of release of acid-soluble nucleotide was similar in both cell types. Production of mono- and oligonucleosomes by micrococcal nuclease as determined by gel electrophoresis also failed to reveal differences in chromatin structure between control and ataxia-telangiectasia cells. Radiation exposure did not significantly alter the kinetics of digestion. These results indicate that there are no gross alterations in chromatin structure in ataxia-telangiectasia cells. 相似文献
254.
The structural gene for the mitochondrial aldehyde dehydrogenase maps to human chromosome 12 总被引:1,自引:1,他引:0
T. Braun K. H. Grzeschik E. Bober S. Singh D. P. Agarwal H. W. Goedde 《Human genetics》1986,73(4):365-367
Summary A cloned 850 bp cDNA fragment corresponding to the 3-coding part of human ALDHI-mRNA was used as a probe for the chromosomal assignment of the ALDHI gene. Southern blot analysis of human-rodent somatic cell hybrids indicates that the human ALDHI gene resides on chromosome 12.Dedicated to Prof. Dr. H. Holzer on the occasion of his 65. birthday 相似文献
255.
Summary Probes of uncloned Bkm satellite DNA and a Drosophila clone 2(8), consisting mainly of GATA repeasts related to a major sequence component in Bkm, have been used to probe Southern blots of human male and female DNAs obtained from a Caucasian and an Australian aboriginal population and to human chromosomes in situ. Hybridization was observed to a distinct and an indistint series of bands against a smeared background. The same distinct bands are identified in the DNA samples with both probes, but are most readily detected using the uncloned Bkm probe. Most restriction bands are common to both populations and some are polymorphic. However, certain bands appear to be characteristic of the Australian aboriginal samples. There are no distinct sex-linked patterns. However all of the small acrocentric human chromosomes, including the Y chromosome show hybridization to uncloned Bkm in situ. 相似文献
256.
Glutamine synthetase (GS) activities of Rhizobia were chromatographically resolved into three distinct forms, GSI, GSII, and GSIII on DEAE cellulose, being eluted with 0.3M, 0.5M and 0.8M KCl, respectively. GSIII was the major form inR. leguminosarum andR. phaseoli. InR. meliloti, however, GSI was the major form. The three forms of GS were also distinguished on the basis of (a) rapid heat inactivation of GSII, (b) insensitivity of GSI to inhibitors, (c) marked inhibition of GSII by thymidine, and (d) inability of Zn++ to inhibit GSIII. The three forms of GS are also distinct molecular entities and are unique to Rhizobia. 相似文献
257.
The essential oil from the fruits of Trachyspermum ammi exhibited toxicity at 800 ppm against Aspergillus flavus and A. niger, the nature of toxicity being cidal. The toxicity of the oil was not affected by autoclaving, temperature treatment and storage upto 365 days. The oil killed the test fungi within 50 seconds; withstood heavy inoculum density and was inhibitory to as many as 21 fungi at its minimum inhibitory concentration. However the seeds of Arachis hypogea whentreated with oil at 5000 ppm and stored for 12 months did not show the appearance of any fungi indicating thereby the grain protectant activity of the oil. The oil was characterized by various physico chemical properties and on chemical investigation Thymol and p-cymene were isolated as antifungal principles of the oil exhibiting toxicity against the test fungi at 1000 ppm. 相似文献
258.
The witches' broom disease has been recently observed on poplars in Paris and its suburbs. The incidence of the disease appeared to be considerably high along main roads. The electron microscopic examination of 350 nm thick sieve tube sections revealed the presence of wall-less mycoplasmalike organisms (MLOs) in diseased samples of Populus alba var. nivea Wesm. They could not be found in their healthy counterparts. 相似文献
259.
S Macura N G Kumar L R Brown 《Biochemical and biophysical research communications》1983,117(2):486-492
Two-dimensional single quantum correlation NMR spectroscopy (COSY) and two-dimensional double quantum NMR spectroscopy (2QT) are used to study spin systems in the 1H NMR spectrum of polymyxin B. Because of different frequency relationships, the two types of two-dimensional NMR experiments are found to be highly complementary. This is demonstrated by combined use of COSY and 2QT spectroscopy to obtain a complete analysis of the complicated spectral overlap which occurs in the 1H NMR spectrum of polymyxin B. 相似文献
260.
Molecular asymmetry in alkaline phosphatase of Escherichia coli 总被引:1,自引:0,他引:1
Thermal inactivation of alkaline phosphatase of Escherichia coli has been studied at different temperatures (45 to 70 degrees C) and pHs (7.5, 9.0, and 10.0) for the commercial, buffer-dialyzed (pH 9.0) and EDTA-dialyzed (pH 9.0) enzymes. In each case, the inactivation exhibits biphasic kinetics consistent with the rate equation, (formula; see text) where A0 and A are activities at time zero and t, and k1 and k2 are first-order rate constants for the fast and slow phase, respectively. Values of k1 and k2 change independently with temperature, pH, and pretreatment (dialysis) of the enzyme. Time course of inactivation of the enzyme with excess EDTA and effect of Zn2+ ion concentration on the activity of EDTA-dialyzed enzyme have been investigated. The data suggest that the dimeric enzyme protein has two types of catalytic sites which have equal catalytic efficiency (or specific activity) but differ in several other properties. Structural implications of these results have been discussed. 相似文献