全文获取类型
收费全文 | 289614篇 |
免费 | 35780篇 |
国内免费 | 198篇 |
专业分类
325592篇 |
出版年
2016年 | 2787篇 |
2015年 | 4156篇 |
2014年 | 4845篇 |
2013年 | 6892篇 |
2012年 | 7755篇 |
2011年 | 7696篇 |
2010年 | 5287篇 |
2009年 | 4985篇 |
2008年 | 7002篇 |
2007年 | 7212篇 |
2006年 | 6838篇 |
2005年 | 6791篇 |
2004年 | 6610篇 |
2003年 | 6722篇 |
2002年 | 6392篇 |
2001年 | 11040篇 |
2000年 | 11155篇 |
1999年 | 9184篇 |
1998年 | 3558篇 |
1997年 | 3730篇 |
1996年 | 3715篇 |
1995年 | 3457篇 |
1994年 | 3458篇 |
1993年 | 3426篇 |
1992年 | 8169篇 |
1991年 | 7958篇 |
1990年 | 7755篇 |
1989年 | 7680篇 |
1988年 | 7245篇 |
1987年 | 7197篇 |
1986年 | 6662篇 |
1985年 | 6811篇 |
1984年 | 5711篇 |
1983年 | 5125篇 |
1982年 | 4092篇 |
1981年 | 3937篇 |
1980年 | 3573篇 |
1979年 | 5924篇 |
1978年 | 4635篇 |
1977年 | 4440篇 |
1976年 | 4235篇 |
1975年 | 4577篇 |
1974年 | 5036篇 |
1973年 | 4927篇 |
1972年 | 4585篇 |
1971年 | 4135篇 |
1970年 | 3643篇 |
1969年 | 3667篇 |
1968年 | 3270篇 |
1967年 | 2823篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
841.
Immunochemical studies on human monoclonal macroglobulins with specificities for 3,4-pyruvylated D-galactose and 4,6-pyruvylated D-glucose 总被引:4,自引:0,他引:4
A S Rao J Liao E A Kabat E F Osserman M Harboe W Nimmich 《The Journal of biological chemistry》1984,259(2):1018-1026
Four of six human monoclonal IgM proteins were found to react best with Klebsiella polysaccharides containing 3,4py beta DGal (pyruvic acetalated D-galactopyranose), one with Klebsiella polysaccharides with 4,6pyDGlc; the sixth is uncharacterized. The combining sites of two of these (IgMWEA and IgMNAE) were essentially indistinguishable by quantitative precipitin studies at varying pH and by quantitative precipitin inhibition assays, but the other two differed in specificity of their combining sites from these and from each other. These differences were detected by precipitin inhibition assays with 3,4py beta DGal-containing oligosaccharide alditols, the R and S isomers of methyl 4,6py alpha DGal, the R isomer of methyl 4,6py beta DGal, or the R and S isomers of methyl 4,6py alpha DGlc, and -beta DGlc. In all of these except the S isomer of methyl 4,6pyDGal and R isomer of methyl 4,6pyDGlc, the carboxyl group is axial to the plane of the acetal ring. Their specificity appears to be determined by the nonreducing ends of chains and is considered to be cavity-type. 相似文献
842.
W Brandst?dter 《Folia haematologica (Leipzig, Germany : 1928)》1982,109(6):843-848
A report is presented on the results of investigations made in 188 657 prospective blood donors from 1974-1980 within the district of Magdeburg. Methods of investigation and recommendations of the International Society of Blood Transfusion for selecting blood donors are compared. A total of 12337 (= 6.53%) were not admitted as a donor and 1360 blood conserves (0.77%) could not be used for transfusion because of laboratory findings obtained afterwards. Causes are dealt with in detail. The necessity of supervising the health of donors and the existing limitations for it are pointed out. 相似文献
843.
844.
G Gluth D Freitag W Hanke F Korte 《Comp. Biochem. Physiol. C, Comp. Pharmacol. Toxicol.》1985,81(2):273-277
The amount of radioactivity which derived from 14C-labeled pollutants was determined in liver, kidney, intestine, blood, muscle and gills of carp, exposed for 6, 24 and 72 hr to high external concentrations of urea, methanol, atrazine and PCP. The results allowed one to calculate roughly the uptake rate for these compounds. It was low for urea (0.055 micrograms/g per hr), higher for methanol (0.12) and atrazine (0.16) and highest for PCP (1.5). The bioaccumulation factors (BFs) were determined for the different substances and organs. They correlated with the hydrophilic-lipophilic nature of the chemicals. The more lipophilic the substances the more accumulation occurred in the liver. PCP accumulated the most. BF was 300-400 in most tissues except muscle where it was quite low. The BF was 3-4 for atrazine in liver, kidney and intestine, but just 1 in blood, muscle and gills. There is some evidence that the BF for methanol equals 1 in liver, kidney, gills and intestine. It is less than 1 in blood and muscle. Urea was equally distributed in all organs and in the external medium. 相似文献
845.
ABSTRACT. Worker bees recently denied access to their colony expose their Nasonov glands, thereby releasing pheromone, at the entrance to their hive. Odours of the following induced this response: empty comb, purified beeswax, honey, pollen, propolis, a live queen, the (E)-9-hydroxy-2-decenoic acid component of a queen's mandibular glands, live drones and workers, inert material on which workers had walked inside the hive, and synthetic Nasonov pheromone. The total odour of a foreign colony also induced worker bees to expose their Nasonov glands but was less effective than the odour of their own colony. Odours of the following were not effective: the (E)-9-oxo-2-decenoic acid component of a queen's mandibular glands, recently killed drones and workers, worker brood (eggs, larvae, pupae). 相似文献
846.
Determination of the molecular mass of bacterial genomic DNA and plasmid copy number by high-pressure liquid chromatography 总被引:1,自引:0,他引:1
Relatively rapid methods for the determination of relative genome molecular mass (Mr) and the estimation of plasmid copy number have been developed. These methods are based on the ability of the Bio-Rad high-pressure liquid chromatography hydroxylapatite column to separate and quantify single-stranded DNA, double-stranded DNA, and plasmid DNA. Genome Mr values were calculated from reassociation kinetics of single-stranded DNA as measured with the hydroxylapatite column. Bacteriophage T4 DNA was used to establish a C0t (moles of nucleotides times seconds per liter), or standard reassociation value. From this C0t value, C0t values for Escherichia coli B, Beggiatoa alba B18LD, and Streptomyces coelicolor were determined by comparative calculations. From those calculated C0t values, the Mr values of 1.96 X 10(9) for E. coli, 2.02 X 10(9) for B. alba, and 3.28 X 10(9) for S. coelicolor were estimated. Plasmid concentration was determined from cleared lysates by comparing the integrated area under the phosphate buffer-eluted plasmid peak to values obtained with known amounts of plasmid. The plasmid copy number was estimated by multiplying the ratio between the amounts of plasmid and chromosomal DNA by the ratio between the Mr values of the chromosome and the plasmid. A copy number of 29 was obtained from a culture of E. coli HB101 harboring pBR322 grown to a culture density of 1.6 X 10(9) CFU . ml-1. 相似文献
847.
Edmund H. Frank Boyce W. Burge Boleslaw H. Liwnicz Linda J. Lotspeich Jocelyn C. White Steven L. Wechsler Frank H. Mayfield Jeffrey T. Keller 《Experimental cell research》1983,146(2):371-376
Cells from cranial and spinal arachnoid membranes of humans were grown in culture. Their growth characteristics, morphology and details of their cytoskeletal composition are described. Arachnoid membranes, obtained at autopsy, were finely minced and incubated in tissue culture medium. Monolayers of cells of homogeneous morphology grew from these tissue fragments. The cells were flat and polygonal. They divided slowly to form non-overlapping monolayers of low cell density. Electron microscopic examination of cultured arachnoid cells revealed numerous desmosome-like tight junctions and abundant intermediate filaments (tonofilaments). Both morphological features are characteristic of arachnoid cells in situ, but not of cells in the fibroblast-rich dura mater. Immunofluorescence microscopy with monoclonal antibodies demonstrated cytokeratin in the cytoplasm of primary cultures of arachnoid cells. Thus we demonstrated that these cultured cells retained certain of the specific differentiated properties of arachnoid cells in situ and that they are not fibroblasts (which lack tight junctions and cytokeratins). To our knowledge, there have been no previous reports of in vitro growth of arachnoid cells. This in vitro model should be useful in studying the response of arachnoid cells to a variety of substances thought to be involved in the chronic inflammatory condition of the meninges known as arachnoiditis. 相似文献
848.
849.
850.