全文获取类型
收费全文 | 14324篇 |
免费 | 1102篇 |
国内免费 | 376篇 |
出版年
2023年 | 110篇 |
2022年 | 229篇 |
2021年 | 338篇 |
2020年 | 268篇 |
2019年 | 312篇 |
2018年 | 376篇 |
2017年 | 313篇 |
2016年 | 415篇 |
2015年 | 658篇 |
2014年 | 709篇 |
2013年 | 947篇 |
2012年 | 1061篇 |
2011年 | 953篇 |
2010年 | 615篇 |
2009年 | 480篇 |
2008年 | 712篇 |
2007年 | 729篇 |
2006年 | 637篇 |
2005年 | 583篇 |
2004年 | 558篇 |
2003年 | 536篇 |
2002年 | 473篇 |
2001年 | 341篇 |
2000年 | 341篇 |
1999年 | 301篇 |
1998年 | 152篇 |
1997年 | 123篇 |
1996年 | 90篇 |
1995年 | 73篇 |
1994年 | 110篇 |
1993年 | 77篇 |
1992年 | 170篇 |
1991年 | 158篇 |
1990年 | 140篇 |
1989年 | 160篇 |
1988年 | 129篇 |
1987年 | 119篇 |
1986年 | 114篇 |
1985年 | 114篇 |
1984年 | 85篇 |
1983年 | 85篇 |
1982年 | 59篇 |
1981年 | 54篇 |
1979年 | 68篇 |
1977年 | 82篇 |
1976年 | 58篇 |
1975年 | 53篇 |
1974年 | 67篇 |
1973年 | 52篇 |
1969年 | 46篇 |
排序方式: 共有10000条查询结果,搜索用时 375 毫秒
991.
Campobasso CP Di Vella G Introna F 《Bollettino della Società italiana di biologia sperimentale》1998,74(7-8):75-82
There are very few papers in forensic literature in which scapular dimensions have been used for estimation of living stature. Allowing the forensic duty to estimate the living stature of skeletal remains, using intact or fragmented scapulae, the Authors have performed multiple regression analysis between the measurements taken from 80 scapula (40 male and 40 female) belonging to a skeletal collection with anthropometric known data. Seven parameters (max length, max breadth, max acrocoracoid distance, length of acromion, max length of coracoid, length of glenoid cavity, width of glenoid cavity) have been recorded. By statistical analysis multiple and linear regressions have been obtained. The results show that living stature may be determined by using regression formulae of single or associated parameters taken from whole or fragmented scapulae. In absence of intact or fragmented long limb bones, scapula sample can be reliably employed for the estimation of stature in forensic practice. 相似文献
992.
Francesca Catanzano Giuseppe Graziano Valeria Cafaro Giuseppe D’Alessio Alberto Di Donato Guido Barone 《International journal of biological macromolecules》1998,23(4):277-285
Four residues Pro19, Leu28, Cys31 and Cys32 proved to be the minimal structural requirements in determining the dimeric structure and the N-terminal segment swapping of bovine seminal ribonuclease, BS-RNase. We analyzed the content of secondary and tertiary structures in RNase A, P-RNase A, PL-RNase A, MCAM-PLCC-RNase A and MCAM-BS-RNase, performing near and far-UV CD spectra. It results that the five proteins have very similar native conformations. Thermal denaturation at pH 5.0 of the proteins, studied by means of CD measurements, proved reversible and well represented by the two-state ND transition model. Thermodynamic data are discussed in the light of the structural information available for RNase A and BS-RNase. 相似文献
993.
Hematopoietic growth factors in autologous transplantation 总被引:1,自引:0,他引:1
Hematopoietic growth factors (HGFs) sustain the survival, proliferation and differentiation of hematopoietic stem cells and
some functions of mature blood cells. In man several HGFs have been characterised and cloned so far, and this has allowed
investigators to confer the rationale for the clinical application of these molecules in hematology and oncology. In particular
G-CSF and GM-CSF are currently utilised to abrogate the hematological toxicity of chemotherapy for standard and dose-intensified
therapy, neutropenia following bone marrow and peripheral blood stem cell transplantation. Moreover there has recently been
great interest in the ex vivo expansion of hematopoietic stem and progenitor cells for a variety of applications, such as
in vitro tumor cell purging or for reducing the volume of blood processed by the leukapheresis. Several combinations of HGFs
have been described to sustain the ex vivo survival and proliferation of these cells disclosing new opportunities in the field
of stem cells transplants. 相似文献
994.
Biogenesis and function of the lipidic structures of pollen grains 总被引:31,自引:0,他引:31
Pollen grains contain several lipidic structures, which play a key role in their development as male gametophytes. The elaborate
extracellular pollen wall, the exine, is largely formed from acyl lipid and phenylpropanoid precursors, which together form
the exceptionally stable biopolymer sporopollenin. An additional extracellular lipidic matrix, the pollen coat, which is particularly
prominent in entomophilous plants, covers the interstices of the exine and has many important functions in pollen dispersal
and pollen-stigma recognition. The sporopollenin and pollen coat precursors are both synthesised in the tapetum under the
control of the sporophytic genome, but at different stages of development. Pollen grains also contain two major intracellular
lipidic structures, namely storage oil bodies and an extensive membrane network. These intracellular lipids are synthesised
in the vegetative cell of the pollen grain under the control of the gametophytic genome. Over the past few years there has
been significant progress in elucidating the composition, biogenesis and function of these important pollen structures. The
purpose of this review is to describe these recent advances within the historical context of research into pollen development.
Received: 1 November 1997 / Revision accepted: 3 February 1998 相似文献
995.
G. Fisher Ph.D. N. Lorenzo H. Abe E. Fujita W. H. Frey C. Emory M. M. Di Fiore A. D'Aniello 《Amino acids》1998,15(3):263-269
Summary Free D-Ser, D-Asp and total D-amino acids were significantly higher (p < 0.05) in Alzheimer (AD) ventricular CSF than in normal CSF. There was no significant difference in the total L-amino acids between AD and normal CSF, but L-Gln and L-His were significantly higher (p < 0.05) in ADCSF. The higher concentrations of these D- and L-amino acids in AD ventricular CSF could reflect the degenerative process that occurs in Alzheimer's brain since ventricular CSF is the repository of amino acids from the brain. 相似文献
996.
997.
L H Faccioli A I Medeiros A Malheiro R C Pietro A Januário B B Vargaftig 《Mediators of inflammation》1998,7(1):41-47
Serum and BALF (bronchoalveolar lavage fluid) IL-8 levels and serum levels were investigated in Toxocara canis infected guinea-pigs and the role of IL-5 as a modulator of cytokine secretion was studied. Serum levels increased early in infected animals, exceeding control levels 4 h after infection, peaked between days 6 and 18, and continued to exceed control levels after 48 days of infection. Serum and BALF IL-8 levels showed the same profile as blood eosinophilia, increasing 6 days post-infection and peaking between days 18 and 24. Treatment of infected animals with anti-IL-5 Ab suppressed eosinophilia with a parallel increase in blood IL-8 levels, whereas no change was found in levels. To support our in vivo observation we carried out experiments in vitro using guinea-pig LPS-stimulated adherent peritoneal cells which release large amounts of IL-8 into the supernatants. When rIL-5 was added to LPS-stimulated cells, 65% inhibition of IL-8 release into the supernatants was observed. Pre-incubation of cells with anti-IL-5 Ab prevented the inhibition of IL-8 release into the supernatants induced by rIL-5. Our results demonstrate for the first time that TNF-alpha and IL-8 are released concomitant with or after IL-5 in the eosinophilic inflammation induced by T. canis. Moreover, in addition to showing that IL-5 is fundamental for the induction of blood eosinophilia, the present results suggest that this cytokine may play a new biological role by acting as modulator of IL-8 secretion. 相似文献
998.
大鼠催乳素基因真核细胞可表达性质粒的构建及应用研究 总被引:4,自引:0,他引:4
735bp的PRLcDNA片段从质粒PRL-SP65#1中回收后,用粘性末端连接法将其重组到真核表达载体pcDNA3上,筛选出正向连接重组体pcDNA3-PRLS和反向连接重组体pcDNA3-PRLAS。将重组体pcDNA3-PRLs和空载体pcDNA3分别转入NIH3T3细胞系,用G418筛选出阳性细胞后与未转染的NIH3T3细胞在加E2和不加E2的情况下,用原位杂交的方法,分别用PRLcDNA探针和原癌基因c-H-rascDNA探针进行检测,未转染的NIH3T3细胞在加E2和不加E2时都几乎无催乳素基因的表达,同样,转入空载体的NIH3T3细胞也无PRL的表达,而转入重组体pcDNA3-PRLS的NIH3T3细胞则有大量的PRL基因的表达,与对照组相比有显著差异(P<0.01)。正常和转入空载体的NIH3T3细胞有一定程度的原癌基因c-H-ras的表达,当分别加入E2和转入重组体pcDNA3-PRLS后,NIH3T3细胞中的c-H-ras基因表达水平都显著升高(P<0.05)。 相似文献
999.
经一系列试验证实百日咳菌大罐培养浓度的下降与培养基中不耐热营养因子不足有关,将培养基的高压灭菌方式改为除菌过滤,保留热不稳定营养因子,可以提高百日咳菌大罐培养浓度;优化酸沉淀条件后,提高了菌苗回收率,从而节省了大量培养基,缩短了生产时间,获得了良好的经济效益。 相似文献
1000.
The relationship among transfer and expression of auxin binding protein gene (abp), auxin (NAA)-induced plasmalemma hyperpolarity and sensibility to auxin during protoplast culture was studied by measuring transmembrane potential difference (Em) and culturing the protoplasts of sense and antisenseabp transgenic tobacco. The concentration of NAA inducing the highest degree of hyperpolarity of senseabp transgenic tobacco protoplasts was lower than the control, and in protoplast culture, their sensibility to auxin increased. The concentration of antisenseabp transgenic tobacco protoplasts was higher than the control, and in protoplast culture, their sensibility to auxin decreased. These results demonstrated that ABP synthesized in endoplasmic reticulum needed to transport to cell membrane and functioned there. 相似文献