全文获取类型
收费全文 | 4925篇 |
免费 | 500篇 |
国内免费 | 26篇 |
专业分类
耳鼻咽喉 | 45篇 |
儿科学 | 131篇 |
妇产科学 | 119篇 |
基础医学 | 744篇 |
口腔科学 | 60篇 |
临床医学 | 561篇 |
内科学 | 805篇 |
皮肤病学 | 47篇 |
神经病学 | 433篇 |
特种医学 | 321篇 |
外科学 | 691篇 |
综合类 | 107篇 |
一般理论 | 2篇 |
预防医学 | 475篇 |
眼科学 | 64篇 |
药学 | 457篇 |
中国医学 | 3篇 |
肿瘤学 | 386篇 |
出版年
2021年 | 55篇 |
2020年 | 36篇 |
2019年 | 59篇 |
2018年 | 73篇 |
2017年 | 56篇 |
2016年 | 63篇 |
2015年 | 82篇 |
2014年 | 108篇 |
2013年 | 154篇 |
2012年 | 228篇 |
2011年 | 195篇 |
2010年 | 125篇 |
2009年 | 98篇 |
2008年 | 166篇 |
2007年 | 213篇 |
2006年 | 188篇 |
2005年 | 185篇 |
2004年 | 171篇 |
2003年 | 164篇 |
2002年 | 147篇 |
2001年 | 183篇 |
2000年 | 172篇 |
1999年 | 120篇 |
1998年 | 93篇 |
1997年 | 107篇 |
1996年 | 96篇 |
1995年 | 77篇 |
1994年 | 68篇 |
1993年 | 66篇 |
1992年 | 142篇 |
1991年 | 130篇 |
1990年 | 120篇 |
1989年 | 143篇 |
1988年 | 137篇 |
1987年 | 105篇 |
1986年 | 86篇 |
1985年 | 98篇 |
1984年 | 76篇 |
1983年 | 48篇 |
1982年 | 49篇 |
1981年 | 36篇 |
1980年 | 48篇 |
1979年 | 53篇 |
1978年 | 57篇 |
1977年 | 49篇 |
1976年 | 40篇 |
1975年 | 46篇 |
1974年 | 40篇 |
1973年 | 36篇 |
1971年 | 38篇 |
排序方式: 共有5451条查询结果,搜索用时 15 毫秒
61.
Mating ability differences between flies of different alcohol dehydrogenase (Adh) genotypes have been assessed in the temperature range 15 to 29°C for laboratory-adapted and field-derivedDrosophila melanogaster. Significant differences amongAdh genotypes were detected principally for the laboratory-adapted strains due to departures from random mating associated with heterozygote superiority at the relatively extreme temperature of 29°C, although mating ability differences could not be attributed directly to theAdh locus. The difference between the laboratory and the field populations can be explained by the effects of genetic back-ground manifested in the form of fitness differences, being enhanced for the laboratory-adapted flies as a consequence of the stress of laboratory culture. In contrast with larval survival and development time, laboratory and field flies do not differe appreciably in their overall abilities to obtain mates, which indicates that mating ability is a direct fitness character not greatly affected by laboratory culture. It follows that direct fitness traits are the least amenable to change under domestication. 相似文献
62.
Left and right, palmar and dorsal skin conductance levels (SCLs) were obtained from hospital controls, left hemisphere lesion Ss, right hemisphere lesion Ss, and diffuse or bilateral lesion Ss during several experimental conditions involving rest, passive auditory stimulation, motor reactions, and simple “perception”. The unilateral lesion groups generally displayed significantly higher palmar SCLs on the side contralateral to their lesion. Such “laterality” was not demonstrated in dorsal recordings or in the hospital controls or diffuse lesion group. These unilateral lesion groups had higher palmar SCLs during passive stimulation than during rest, motor, or perception phases. Results were discussed in terms of possible neural mechanisms underlying the phenomena. 相似文献
63.
Oligopeptidases of brush border membranes of rat small intestinal mucosal cells 总被引:5,自引:1,他引:5
下载免费PDF全文
![点击此处可从《The Journal of physiology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
1. The properties of peptidases located in the brush borders of rat small intestinal mucosal cells have been investigated using a new method for the assay of peptidase activity. In this method amino acids produced by hydrolysis of peptides are oxidized by ophidian L-amino acid oxidase and the hydrogen peroxide produced during reoxidation of the reduced enzyme is estimated spectrophotometrically.2. 10-20% of the total cellular peptidase activity and 50% of the leucylnaphthylamidase (LNAase) activity were found to be tightly bound to the brush borders and to possess different substrate specificity from the supernatant peptidase activity.3. Evidence from kinetic and competition studies indicates the presence of more than one peptidase in the brush borders. The peptidases exhibit pH optima of 8.0-8.5, are inhibited by EDTA, but are not usually activated by divalent metal ions. The brush border peptidases hydrolyse di- and tripeptides, some oligopeptides, leucinamide and leucyl-beta-naphthylamine. On the basis of the Michaelis constants, these substrates differ in their affinities for the enzymes.4. It is proposed that the brush border peptidases serve an analogous function in the terminal stages of protein digestion to that of the disaccharidases in the case of carbohydrate digestion and absorption. 相似文献
64.
Detection of human immunodeficiency virus type 1 (HIV-1) DNA and RNA sequences in HIV-1 antibody-positive blood donors in Uganda by the Roche AMPLICOR assay.
下载免费PDF全文
![点击此处可从《Journal of clinical microbiology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
J B Jackson E M Piwowar J Parsons P Kataaha G Bihibwa J Onecan S Kabengera S D Kennedy A Butcher 《Journal of clinical microbiology》1997,35(4):873-876
The ability of commercially available PCR-based assays to accurately detect or quantitate human immunodeficiency virus type 1 (HIV-1) DNA or RNA in individuals predominantly infected with HIV-1 subtypes A and D is not known. Therefore, peripheral leukocytes from 43 individuals in Kampala, Uganda, positive for HIV by the Western blot (immunoblot) assay were tested by using the Roche AMPLICOR HIV-1 assay for the detection of DNA gag sequences. Plasma from these same individuals was tested by using the Roche HIV-1 AMPLICOR MONITOR HIV-1 assay for the quantitation of HIV-1 RNA gag sequences. In addition, peripheral leukocytes were tested for HIV-1 DNA by using a lower annealing temperature or a different primer pair for the HIV-1 pol region. The proportions of individuals with detectable HIV-1 DNA and RNA gag sequences by the Roche assays were 74 and 90%, respectively. The proportions positive for HIV-1 DNA sequences by using a 50 degrees C annealing temperature or the pol primer pair were 71 and 98%, respectively. In summary, the standard Roche assay did not detect HIV-1 DNA sequences in a significant number of HIV-1-infected individuals in Uganda. However, use of a pol primer pair increased the sensitivity of the assay to 98%. The sensitivity of the Roche AMPLICOR MONITOR assay for the detection and quantitation of HIV-1 RNA sequences was significantly higher than that of the DNA-based assay, but the efficiency of the assay, and hence, the accuracy of the values obtained with RNA, is not known. Modifications to existing assays are needed to enhance the sensitivities and accuracies of these commercially available assays for use in developing countries where non-B HIV-1 subtypes predominate. 相似文献
65.
The ratio of 2nd to 4th digit length: a predictor of sperm numbers and concentrations of testosterone, luteinizing hormone and oestrogen 总被引:19,自引:2,他引:19
Manning JT; Scutt D; Wilson J; Lewis-Jones DI 《Human reproduction (Oxford, England)》1998,13(11):3000-3004
The differentiation of the urinogenital system and the appendicular
skeleton in vertebrates is under the control of Hox genes. The common
control of digit and gonad differentiation raises the possibility that
patterns of digit formation may relate to spermatogenesis and hormonal
concentrations. This work was concerned with the ratio between the length
of the 2nd and 4th digit (2D:4D) in humans. We showed that (i) 2D:4D in
right and left hands has a sexually dimorphic pattern; in males mean 2D:4D
= 0.98, i.e. the 4th digit tended to be longer than the 2nd and in females
mean 2D:4D = 1.00, i.e. the 2nd and 4th digits tended to be of equal
length. The dimorphism is present from at least age 2 years and 2D:4D is
probably established in utero; (ii) high 2D:4D ratio in right hands was
associated with germ cell failure in men (P = 0.04); (iii) sperm number was
negatively related to 2D:4D in the right hand (P = 0.004); (iv) in men
testosterone concentrations were negatively related to right hand 2D:4D and
in women and men LH (right hand), oestrogen (right and left hands) and
prolactin (right hand) concentrations were positively correlated with 2D:4D
ratio and (v) 2D:4D ratio in right hands remained positively related to
luteinizing hormone and oestrogen after controlling for sex, age, height
and weight.
相似文献
66.
67.
Hart TC; Bowden DW; Bolyard J; Kula K; Hall K; Wright JT 《Human molecular genetics》1997,6(13):2279-2284
Tricho-dento-osseous syndrome (TDO), MIM# 190320, is transmitted as a
highly penetrant autosomal dominant trait that is characterized by variable
clinical expression. The principal clinical features include kinky/curly
hair in infancy, enamel hypoplasia, taurodontism, as well as increased
thickness and density of cranial bones. Possible genetic linkage has been
reported for TDO with the ABO blood group locus, but the gene defect
remains unknown. We have identified four multiplex families (n = 63, 39
affected, 24 unaffected) from North Carolina segregating TDO. We previously
have excluded a major locus for TDO in the ABO region for these families.
Utilizing a genome-wide search strategy, we obtained conclusive evidence
for linkage of the TDO syndrome locus to markers on chromosome 17q21
(D17S791, Z max = 10.54, Theta = 0.00) with no indication of genetic
heterogeneity. Multipoint analysis suggests the TDO locus is located in a 7
cM chromosomal segment flanked by D17S932 and D17S941. This finding
represents the first step towards isolation and cloning of the TDO gene.
Identification of this gene has important implications for understanding
normal and abnormal craniofacial development of hair, teeth and bone.
相似文献
68.
Lactate production in isolated perfused rat lung 总被引:1,自引:0,他引:1
69.
We have used a rabbit antiserum directed against a portion of the MC29 viral myc protein expressed in bacteria to characterize the cellular myc protein from three different avian bursal lymphoma cell lines (1104HI, 1104BI S13, BK25), and from normal chick embryo cells. The phosphorylated myc proteins immunoprecipitated from these cells varied in molecular weight from 58 to 62 kDa and localized to the cell nucleus, as shown by cell fractionation experiments. Pulse-chase experiments established that these proteins had short half-lives ranging from 12 min for the myc proteins from the 1104BI S13 cell line to 25 min for myc proteins from both the 1104HI and the BK25 cell lines. The structural relatedness of the proteins was established by comparing their partial proteolytic digestion products (Cleveland analysis) with the partial proteolytic digestion products of the MH2 viral myc protein. The anti-myc-serum also immunoprecipitated a 48-kDa protein from each of the bursal cell lines. We have identified this protein as a breakdown product of the bursal cell myc proteins. The different size and number of these bursal cell myc proteins may be a direct result of the specific site of integration as well as the orientation of the retrovirus LTR sequence relative to the adjacent cellular myc allele. 相似文献
70.
M Parsons M Valentine J Deans G L Schieven J A Ledbetter 《Molecular and biochemical parasitology》1991,45(2):241-248
Regulation of tyrosine phosphorylation is a critical element in controlling growth and differentiation in higher eukaryotes. We have determined that the protozoan Trypanosoma brucei, which diverged early in the eukaryotic lineage, possesses multiple proteins which react with a specific anti-phosphotyrosine antiserum. Anti-phosphotyrosine immunoprecipitates of [32P]orthophosphate-labeled cells were shown to contain phosphotyrosine by two-dimensional electrophoresis. Western analysis of cells from different stages of the life cycle demonstrates the appearance of tyrosine-phosphorylated proteins at 40-42 kDa during the transition from slender to stumpy blood-forms. Growth of procyclic form cells in orthovanadate resulted in increased levels of specific tyrosine-phosphorylated proteins. The demonstration of phosphotyrosine-containing proteins in T. brucei and their differential regulation during the life cycle suggests that tyrosine kinases and phosphatases may play an important role in the biology of primitive protozoa. 相似文献