全文获取类型
收费全文 | 429784篇 |
免费 | 7063篇 |
国内免费 | 2410篇 |
专业分类
电工技术 | 8559篇 |
技术理论 | 5篇 |
综合类 | 1396篇 |
化学工业 | 69007篇 |
金属工艺 | 17872篇 |
机械仪表 | 12440篇 |
建筑科学 | 10984篇 |
矿业工程 | 2558篇 |
能源动力 | 9922篇 |
轻工业 | 41782篇 |
水利工程 | 4404篇 |
石油天然气 | 8608篇 |
武器工业 | 251篇 |
无线电 | 45183篇 |
一般工业技术 | 80481篇 |
冶金工业 | 80914篇 |
原子能技术 | 9111篇 |
自动化技术 | 35780篇 |
出版年
2021年 | 4003篇 |
2019年 | 3437篇 |
2018年 | 5720篇 |
2017年 | 5648篇 |
2016年 | 6175篇 |
2015年 | 4752篇 |
2014年 | 7463篇 |
2013年 | 19244篇 |
2012年 | 12362篇 |
2011年 | 16329篇 |
2010年 | 13083篇 |
2009年 | 14285篇 |
2008年 | 15074篇 |
2007年 | 15213篇 |
2006年 | 13091篇 |
2005年 | 11690篇 |
2004年 | 10645篇 |
2003年 | 9960篇 |
2002年 | 9930篇 |
2001年 | 9913篇 |
2000年 | 9379篇 |
1999年 | 9552篇 |
1998年 | 23230篇 |
1997年 | 16727篇 |
1996年 | 12760篇 |
1995年 | 9621篇 |
1994年 | 8481篇 |
1993年 | 8284篇 |
1992年 | 6242篇 |
1991年 | 6018篇 |
1990年 | 5946篇 |
1989年 | 5964篇 |
1988年 | 5634篇 |
1987年 | 4956篇 |
1986年 | 4879篇 |
1985年 | 5613篇 |
1984年 | 5288篇 |
1983年 | 4923篇 |
1982年 | 4393篇 |
1981年 | 4690篇 |
1980年 | 4307篇 |
1979年 | 4435篇 |
1978年 | 4305篇 |
1977年 | 4816篇 |
1976年 | 6395篇 |
1975年 | 3824篇 |
1974年 | 3637篇 |
1973年 | 3766篇 |
1972年 | 3135篇 |
1971年 | 2867篇 |
排序方式: 共有10000条查询结果,搜索用时 9 毫秒
101.
M Vives ME Garcia P Saenz MA Mora L Mata H Sabharwal C Svanborg 《Canadian Metallurgical Quarterly》1997,16(9):852-858
BACKGROUND: The establishment of the nasopharyngeal flora was followed in Costa Rican children from birth to 1 year of age. METHODS: Nasopharyngeal cultures were obtained at 1 (n = 413), 3 (n = 393), 6 (n = 376) and 12 months (n = 356) of age from children representative of the population in the Puriscal district. Weekly cultures were obtained from a subcohort of these children (n = 101). Mother-infant diads (n = 95) and preschool children (n = 208) attending day-care centers were also studied. RESULTS: The estimated proportion of colonized children in the population differed markedly depending on the frequency of culture. Quarterly cultures showed a slow increase in carrier rates from 3.9% for Haemophilus influenzae, 3.1% for Streptococcus pneumoniae and 6.5% for Moraxella catarrhalis at 1 month of age to 10.1% carrying H. influenzae and 19.4% carrying S. pneumoniae by the end of the first year. By quarterly culture the proportion of children colonized at least once was 36% for S. pneumoniae, 26% for H. influenzae and 28% for M. catarrhalis. In contrast weekly sampling showed that 95 to 100% of the children were colonized at least once during the first year of life with H. influenzae, S. pneumoniae or M. catarrhalis. Nasopharyngeal carriage of H. influenzae, S. pneumoniae and M. catarrhalis was low in the mothers, and very few mother-infant pairs carried identical bacteria at the same time. In contrast carrier rates were high in the siblings attending day care (H. influenzae 27.9%, S. pneumoniae 39.4%, both organisms 26.6%). Infants with siblings had significantly higher bacterial carriage at all ages than infants without siblings. CONCLUSIONS: Quarterly nasopharyngeal cultures showed that Costa Rican infants acquire their nasopharyngeal flora at a rate comparable with that for infants in developed countries and that siblings are an important source of the bacteria. Weekly samplings showed that virtually all children were colonized at least once during the first year of life. 相似文献
102.
OBJECTIVE AND DESIGN: We reported previously that the betamethasone derivative betamethasone dipropionate behaves as an anti-glucocorticoid in rat endotoxin-induced uveitis (EIU). In the present study, we produced EIU in guinea pigs and investigated the effects of betamethasone dipropionate on the EIU. MATERIAL: Male Hartley guinea pigs were used. TREATMENT: Glucocorticoids were instilled into the eye. METHOD: To elicit EIU, lipopolysaccharide (LPS) was injected into the anterior chamber of the eye. Cell numbers in the aqueous humor after LPS injection were determined by flow cytometry. Prostaglandin E2 (PGE2) production after LPS injection into the anterior chamber was also examined. RESULTS: Intracameral injection of LPS (1 microgram/eye) induced cell infiltration into the anterior chamber and PGE2 production. Betamethasone dipropionate inhibited cell infiltration and PGE2 production more strongly than betamethasone. These results suggest that betamethasone dipropionate is a potent glucocorticoid in guinea pigs. CONCLUSIONS: Structure-activity relationships of glucocorticoids in the guinea pig EIL model may differ from those in the rat EIU model. 相似文献
103.
The three-dimensional structure of glutathione S-transferase from Arabidopsis thaliana has been solved at 2.2 A resolution (Reinemer et al., 1996). The enzyme forms a dimer of two identical subunits. The structure shows a new G-site architecture and a novel and unique dimer interface. Each monomer of the protein forms a separate G-site. Therefore, the requirements on the dimer interface are reduced. As a consequence, the interactions between the monomers are weaker and residues at the dimer interface are more variable. Thus, the dimer interface looses its relevance for a classification of plant glutathione S-transferases and the formation of heterodimers becomes even more difficult to predict. 相似文献
104.
L Guarente 《Canadian Metallurgical Quarterly》1997,11(19):2449-2455
105.
106.
107.
A Sawicka-Grzelak F Meisel-Miko?ajczyk SM S?otwińska M Wierzbicka 《Canadian Metallurgical Quarterly》1997,49(1-2):95-100
The aim of study was the evaluation of periodontal pockets microflora in patients with advanced periodontitis. From each subject 16-20 samples were taken using paper points. Pooled sample after 60 s. mixing was serially diluted in reduced BHI. For total cell counts and for the isolation of black pigmented anaerobes Brucella agar supplemented with 5% sheep blood, hemin, menadione, with and without Kanamycin-Vancomycin mixture and BM agar plates were used. For isolation of A. actinomycetemcomitans TSBV agar plates were used. Cultures were incubated in anaerobic chamber at 37 degrees C for 7 days and TSBV agar plates in an atmosphere of 95% air-5% CO2 at 37 degrees C for 5 days. Microorganisms were identified by Gram staining, colony morphology, fluorescence in UV-light, haemagglutination of 3% sheep erythrocytes, fermentation of sugars, production of indole, urease (API 20A), specific enzymes (Rapid ID 32A). Twenty seven subjects with clinically recognized periodontitis were examined. Microorganisms important in periodontitis were isolated from periodontal pockets of almost all examined subjects. The number of bacteria obtained from the sample of one patient ranged from 1 x 10(4) CFU/ml to 3,6 x 10(6) CFU/ml. Porphyromonas gingivalis was identified in the samples taken from 17 patients, Prevotella intermedia-19, Actinobacillus actinomycetemcomitans -11, Fusobacterium nucleatum-9, Peptostreptococcus spp.-22. 相似文献
108.
T Reck F K?ckerling C Schneider W Hohenberger 《Canadian Metallurgical Quarterly》1997,122(10):914-918
Morgagni hernias are the least common form of diaphragmatic hernias. Although they are congenital, most of them are not diagnosed until later in life. The indication for surgery is based on the patient's symptoms or on the radiological evidence of incarcerated tissue, and until quite recently involved a laparotomy or thoracotomy. Laparoscopy not only permits the suspected diagnosis to be confirmed--which is otherwise often difficult--but also makes it possible to close the hernia site by suturing. For improved security, the hernia site is augmented by fixing in place a non-absorbable mesh. The operative technique employed is described. 相似文献
109.
110.
Cresswell M.W. Allen R.A. Guthrie W.F. Sniegowski J.J. Ghoshtagore R.N. Linholm L.W. 《Semiconductor Manufacturing, IEEE Transactions on》1998,11(2):182-193
The physical widths of reference features incorporated into electrical linewidth test structures patterned in films of monocrystalline silicon have been determined from Kelvin voltage measurements. The films in which the test structures are patterned are electrically insulated from the bulk-silicon substrate by a layer of silicon dioxide provided by SIMOX (Separation by the IMplantation of OXygen) processing. The motivation is to facilitate the development of linewidth reference materials for critical-dimension (CD) metrology-instrument calibration. The selection of the (110) orientation of the starting silicon and the orientation of the structures' features relative to the crystal lattice enable a lattice-plane-selective etch to generate reference-feature properties of rectangular cross section and atomically planar sidewalls. These properties are highly desirable for CD applications in which feature widths are certified with nanometer-level uncertainty for use by a diverse range of CD instruments. End applications include the development and calibration of new generations of CD instruments directed at controlling processes for manufacturing devices having sub-quarter-micrometer features 相似文献