全文获取类型
收费全文 | 1906篇 |
免费 | 5篇 |
国内免费 | 2篇 |
专业分类
综合类 | 2篇 |
化学工业 | 16篇 |
金属工艺 | 9篇 |
机械仪表 | 6篇 |
建筑科学 | 4篇 |
矿业工程 | 1篇 |
能源动力 | 1篇 |
轻工业 | 21篇 |
石油天然气 | 7篇 |
无线电 | 5篇 |
一般工业技术 | 8篇 |
冶金工业 | 1825篇 |
自动化技术 | 8篇 |
出版年
2021年 | 1篇 |
2020年 | 1篇 |
2019年 | 4篇 |
2018年 | 2篇 |
2017年 | 1篇 |
2016年 | 3篇 |
2015年 | 2篇 |
2014年 | 1篇 |
2013年 | 7篇 |
2012年 | 1篇 |
2011年 | 1篇 |
2009年 | 6篇 |
2008年 | 2篇 |
2007年 | 2篇 |
2006年 | 4篇 |
2005年 | 5篇 |
2004年 | 3篇 |
2003年 | 2篇 |
2002年 | 3篇 |
2000年 | 1篇 |
1999年 | 51篇 |
1998年 | 621篇 |
1997年 | 340篇 |
1996年 | 186篇 |
1995年 | 128篇 |
1994年 | 98篇 |
1993年 | 108篇 |
1992年 | 13篇 |
1991年 | 31篇 |
1990年 | 26篇 |
1989年 | 28篇 |
1988年 | 29篇 |
1987年 | 26篇 |
1986年 | 22篇 |
1985年 | 24篇 |
1984年 | 1篇 |
1983年 | 3篇 |
1982年 | 6篇 |
1981年 | 3篇 |
1980年 | 13篇 |
1978年 | 4篇 |
1977年 | 21篇 |
1976年 | 73篇 |
1973年 | 2篇 |
1965年 | 1篇 |
1934年 | 1篇 |
1933年 | 1篇 |
1929年 | 1篇 |
排序方式: 共有1913条查询结果,搜索用时 15 毫秒
31.
32.
CS Chen M Mrksich S Huang GM Whitesides DE Ingber 《Canadian Metallurgical Quarterly》1998,14(3):356-363
The control of cell position and function is a fundamental focus in the development of applications ranging from cellular biosensors to tissue engineering. Using microcontact printing of self-assembled monolayers (SAMs) of alkanethiolates on gold, we manufactured substrates that contained micrometer-scale islands of extracellular matrix (ECM) separated by nonadhesive regions such that the pattern of islands determined the distribution and position of bovine and human endothelial cells. In addition, the size and geometry of the islands were shown to control cell shape. Traditional approaches to modulate cell shape, either by attaching suspended cells to microbeads of different sizes or by plating cells on substrates coated with different densities of ECM, suggested that cell shape may play an important role in control of apoptosis as well as growth. Data are presented which show how micropatterned substrates were used to definitively test this hypothesis. Progressively restricting bovine and human endothelial cell extension by culturing cells on smaller and smaller micropatterned adhesive islands regulated a transition from growth to apoptosis on a single continuum of cell spreading, thus confirming the central role of cell shape in cell function. The micropatterning technology is therefore essential not only for construction of biosurface devices but also for the investigation of the fundamental biology of cell-ECM interactions. 相似文献
33.
The effect of Pseudomonas aeruginosa infection on clinical parameters in steady-state bronchiectasis
PL Ho KN Chan MS Ip WK Lam CS Ho KY Yuen KW Tsang 《Canadian Metallurgical Quarterly》1998,114(6):1594-1598
STUDY OBJECTIVE: To investigate the effect of Pseudomonas aeruginosa infection on clinical parameters in Chinese patients with noncystic fibrosis and steady-state bronchiectasis. DESIGN: Prospective, cross-sectional clinicomicrobiological study with informed consent. SETTING: Consecutive outpatient recruitment from a specialist bronchiectasis respiratory clinic. PATIENTS: Outpatients (n = 100; 62 women; 55.1+/-16.7 years old; FEV1/FVC 1.4+/-0.7/2.1+/-0.9 L), who had stable respiratory symptoms for more than 3 weeks. MEASUREMENTS AND RESULTS: Respiratory pathogens isolated from the sputum were: Pseudomonas aeruginosa (33), Haemophilus influenzae (10), Moraxella catarrhalis (2), other Gram-negative bacilli (5), Streptococcus pneumoniae (6), Staphylococcus aureus (5), mycobacteria (3), and yeast (1). Clinical parameters in patients with positive isolation of P aeruginosa were compared with those without the organism in the sputum culture (non-P aeruginosa). In the P aeruginosa group, the FEV1/FVC ratio and sputum volume were lower (p < 0.005) and higher (p < 0.0001), respectively, than those of the non-P aeruginosa group. The FEV1/FVC ratio (< 60%) and sputum volume (grading > 5) were independently associated with a positive sputum isolation of P aeruginosa with odds ratios of 3.1 (confidence interval [CI] 1.2 to 8.4; p < 0.01) and 4.7 (CI 1.6 to 13.3; p < 0.001), respectively. CONCLUSIONS: P aeruginosa is the predominant respiratory pathogen isolated in the sputum of Chinese patients with steady-state bronchiectasis, and its isolation is associated with high sputum output (> or = 75th quartile) and moderately severe airflow obstruction (FEV1/FVC < 60%). 相似文献
34.
We examined the effects of different cytokine combinations and culture conditions on the expansion and modulation of cell surface antigens of CD34+ derived dendritic cells (DCs), the most efficient antigen-presenting cells capable of stimulating resting T cells in the primary immune response. Cells with a dendritic morphology and expressing HLA-DR, CD1a, S100 and CD83 were maximally expanded under serum-free conditions with the addition of SCF, GM-CSF, TNF-alpha, TGF-beta and Flt-3 ligand (fold increase of CD1a+ cells = 102 +/- 32 after 2 weeks of culture). CD34+ cells were also grown under continuous flow conditions in an artificial capillary system: after 14d of culture, the expansion in the total cell number was lower than that of the static cultures (3.3 +/- 2 v 18.9 +/- 4) but the percentage of CD1a+/CD83+/ CD80+ cells was considerably higher, whereas the CD14+ cells were significantly reduced (8.9 +/- 2 v 26 +/- 13). In continuous perfusion cultures, low levels of DC precursors and of LTC-IC were still present up to day 14. The DCs generated under flow conditions stimulated the mixed leucocyte reaction (MLR) more than the cells grown in static cultures. By electron microscopy, cells grown in the continuous flow system showed an increased number of large cells with numerous dendritic processes and abundant multilamellar complexes. The cells expanded under these conditions were sorted on the basis of their light-scatter properties into two fractions: one containing a predominance of CD1a+/S100+/ CD8 3+/CD80+/CD14- 'large cells' with great internal complexity (mature DCs); the second including 'small cells' either CD33+/CD14+, CD33+/CD15+ or CD33+/CD13-/CD14. The DCs generated and selected with this method are therefore particularly well suited for immunotherapeutic protocols. 相似文献
35.
Spina bifida, a congenital deformity of the posterior wall of vertebrae of the spine, is a midline defect of skin, vertebral arches and neural tube, usually in the lumbosacral region. Its incidence is reported to be 0.2 to 0.4 per 1000 live births. Various hypotheses have been put forward as etiological factors for spina bifida including consumption of potato affected by blight and hardness of drinking water but these have not been proven. Two groups of 50 randomly chosen children were established. The study group consisted of children aged 5 to 12 years, weighing 15 to 30 kg, consuming fluoride rich drinking water (4.5 and 8.5 ppm fluoride; WHO permissible limit is 1.5 ppm fluoride), and manifesting either clinical, dental and/or skeletal fluorosis. The control group consisted of age and weight-matched children, consuming less than or equal to 1.5 ppm fluoride in drinking water and not showing any evidence of fluoride toxicity. These children were evaluated for antenatal history, general clinical examination (especially for dimples, tufts of hair, haemangioma on skin throughout the length of spine), other congenital abnormalities, evidence of fluoride toxicity, biochemical estimation for fluoride levels in blood and serum and by skiagrams of the spine to examine for the presence of spina bifida occulta. A total of 22 (44%) of the 50 children in group A, the study group, and 6 (12%) of the 50 children in group B, the control group, revealed spina bifida occulta in the lumbosacral region.(ABSTRACT TRUNCATED AT 250 WORDS) 相似文献
36.
37.
38.
Three groups of phosphoproteins have been distinguished, basing on the velocity and extent of phosphorylation in platelets stimulated with collagen. pp60c-src constituted the first group; the increase in its phosphorylation was the highest and most rapid (maximal in 30 s after the addition of collagen). pp80/85 and non-identified protein of 65 kDa formed the second group; the increase in their phosphorylation was twice smaller than that of pp60c-src, and reached its maximum 60 s after the addition of collagen. pp120, pp72syk, and two non-identified phosphoproteins of 90 and 75 kDa constituted the third group; the increase in their phosphorylation was 4-10-fold lower than that of pp60c-src and reached its maximum after 180 s. We conclude that the phosphorylation of pp60c-src is important for the change of shape of platelets, the phosphorylation of pp80/85 and pp65 for the initiation of the formation of aggregates and the phosphorylation of the third group of phosphoproteins for the formation of massive aggregates. This conclusion was supported by using a monoclonal anti-GPIb antibody, which did not inhibit the shape change of platelets and did not inhibit pp60c-src phosphorylation. This antibody inhibited aggregate formation as well as tyrosine phosphorylation of proteins belonging to the second and the third group of phosphoproteins. 相似文献
39.
Women's health centers are often associated with a comprehensive model of health care that treats the "whole woman." Using data from a nationwide study of 467 women's health centers, we explored how the ideal of comprehensive care was implemented with respect to mental health services. Specifically, we examined the rates of screening and treatment for a subset of mental health and behavioral and social problems in women's health centers and the structural, staffing, philosophical, and patient factors associated with the provision of services. Across 12 services, the overall rates of provision ranged from 7.7% for screening for dementing disorders to 27.6% for smoking cessation counseling and treatment. In a series of logistic regressions, center type (primary care) and having a mental health staff person were consistently associated with service provision; other important variables were having a high percentage of women using the center as their usual source of care and having a belief in women-centered care. Findings indicate that the majority of women using women's health centers do not receive services in a comprehensive care environment that includes key mental health services. 相似文献
40.
Rigid body rotation of five domains and movements within their interfacial joints provide a rational context for understanding why HIV protease mutations that arise in drug resistant strains are often spatially removed from the drug or substrate binding sites. Domain motions associated with substrate binding in the retroviral HIV-1 and SIV proteases are identified and characterized. These motions are in addition to closure of the flaps and result from rotations of approximately 6-7 degrees at primarily hydrophobic interfaces. A crystal structure of unliganded SIV protease (incorporating the point mutation Ser 4 His to stabilize the protease against autolysis) was determined to 2.0 A resolution in a new space group, P3221. The structure is in the most "open" conformation of any retroviral protease so far examined, with six residues of the flaps disordered. Comparison of this and unliganded HIV structures, with their respective liganded structures by difference distance matrixes identifies five domains of the protease dimer that move as rigid bodies against one another: one terminal domain encompassing the N- and C-terminal beta sheet of the dimer, two core domains containing the catalytic aspartic acids, and two flap domains. The two core domains rotate toward each other on substrate binding, reshaping the binding pocket. We therefore show that, for enzymes, mutations at interdomain interfaces that favor the unliganded form of the target active site will increase the off-rate of the inhibitor, allowing the substrate greater access for catalysis. This offers a mechanism of resistance to competitive inhibitors, especially when the forward enzymatic reaction rate exceeds the rate of substrate dissociation. 相似文献