全文获取类型
收费全文 | 9559篇 |
免费 | 122篇 |
国内免费 | 9篇 |
专业分类
电工技术 | 97篇 |
综合类 | 2篇 |
化学工业 | 1000篇 |
金属工艺 | 101篇 |
机械仪表 | 301篇 |
建筑科学 | 216篇 |
矿业工程 | 28篇 |
能源动力 | 129篇 |
轻工业 | 868篇 |
水利工程 | 107篇 |
石油天然气 | 15篇 |
无线电 | 863篇 |
一般工业技术 | 1020篇 |
冶金工业 | 4088篇 |
原子能技术 | 108篇 |
自动化技术 | 747篇 |
出版年
2021年 | 67篇 |
2020年 | 51篇 |
2019年 | 61篇 |
2018年 | 60篇 |
2017年 | 82篇 |
2016年 | 66篇 |
2015年 | 47篇 |
2014年 | 104篇 |
2013年 | 315篇 |
2012年 | 160篇 |
2011年 | 237篇 |
2010年 | 211篇 |
2009年 | 231篇 |
2008年 | 260篇 |
2007年 | 239篇 |
2006年 | 245篇 |
2005年 | 218篇 |
2004年 | 179篇 |
2003年 | 199篇 |
2002年 | 201篇 |
2001年 | 162篇 |
2000年 | 160篇 |
1999年 | 219篇 |
1998年 | 1038篇 |
1997年 | 647篇 |
1996年 | 524篇 |
1995年 | 349篇 |
1994年 | 313篇 |
1993年 | 310篇 |
1992年 | 118篇 |
1991年 | 136篇 |
1990年 | 151篇 |
1989年 | 144篇 |
1988年 | 145篇 |
1987年 | 143篇 |
1986年 | 108篇 |
1985年 | 133篇 |
1984年 | 94篇 |
1983年 | 102篇 |
1982年 | 74篇 |
1981年 | 94篇 |
1980年 | 80篇 |
1979年 | 79篇 |
1978年 | 74篇 |
1977年 | 145篇 |
1976年 | 276篇 |
1975年 | 74篇 |
1974年 | 71篇 |
1973年 | 63篇 |
1972年 | 53篇 |
排序方式: 共有9690条查询结果,搜索用时 359 毫秒
111.
HM Trist SG Tyack MA Johnson CT Prideaux M Sheppard 《Canadian Metallurgical Quarterly》1996,40(1):130-139
Restriction enzyme linkage maps were produced for the genomic short region of the virulent infectious laryngotracheitis virus (CSW-1 strain). After comparison with the equivalent restriction enzyme linkage maps for the infectious laryngotracheitis virus SA-2 strain (a vaccine strain), it was determined that the maps for the short regions of the two strains were identical, apart from a single section in each of the inverted terminal repeats. Each inverted terminal repeat of the SA-2 strain was discovered to contain 467 base pairs more DNA than the CSW-1 strain's inverted terminal repeats. This extra DNA was more precisely mapped entirely within the EcoRI fragments D and d of SA-2, which were found to form part of the SmaI fragments U and P of SA-2 and Q and b of SA-2 and to contain one SmaI restriction enzyme site. 相似文献
112.
Despite the fact that the neuroleptic drugs have been widely used for more than 40 years, one of their most common side-effects, akathisia, has been relatively neglected. There are still no universally agreed diagnostic criteria for akathisia, particularly chronic akathisia, and in this review article, we discuss the controversies surrounding the voluntary nature of its motor features and the importance of the dysphoric component. We also review the published epidemiological studies to show the great variation in frequency of occurrence. Finally, we discuss the possible neurotransmitters involved in the pathophysiology and treatment of this condition. 相似文献
113.
CB McCoy SA Smith LR Metsch RS Anwyl R Correa L Bankston JJ Zavertnik 《Canadian Metallurgical Quarterly》1994,2(4):267-274
Socioeconomic status is the most significant factor influencing the decreased survival associated with breast cancer in minority groups in the United States. Barriers to the use of early detection programs by low-income women often result in the detection of breast cancer at stages too advanced to assure optimum outcomes. In an effort to increase accessibility of breast cancer screening among such individuals, the Early Detection Program (EDP) was initiated in 1987. The program provided breast cancer screening to women 40 years of age and older who attended eight primary healthcare centers located in low-income neighborhoods throughout Dade County, Florida. From its inception in October 1987 through December 1993, 23,866 medically underserved women had mammography examinations, with more than 17,000 of these women undergoing baseline mammograms. Since the program's inception, 126 cancers were diagnosed in 123 women. A dramatic shift from later to earlier stage breast cancers was observed. These results warrant a greater inclusion of medically underserved and lower socioeconomic status women in screening programs for the early detection of breast cancer. 相似文献
114.
Pigmentation phenotypes of variant extension locus alleles result from point mutations that alter MSH receptor function 总被引:2,自引:0,他引:2
LS Robbins JH Nadeau KR Johnson MA Kelly L Roselli-Rehfuss E Baack KG Mountjoy RD Cone 《Canadian Metallurgical Quarterly》1993,72(6):827-834
Coat colors in the chestnut horse, the yellow Labrador retriever, the red fox, and one type of yellow mouse are due to recessive alleles at the extension locus. Similarly, dominant alleles at this locus are often responsible for dark coat colors in mammals, such as the melanic form of the leopard, Panthera pardus. We show here that the murine extension locus encodes the melanocyte-stimulating hormone (MSH) receptor. In mice, the recessive yellow allele (e) results from a frameshift that produces a prematurely terminated, nonfunctioning receptor. The sombre (Eso and Eso-3J) and tobacco darkening (Etob) alleles, which both have dominant melanizing effects, results from point mutations that produce hyperactive MSH receptors. The Eso-3J receptor is constitutively activated, while the Etob receptor remains hormone responsive and produces a greater activation of its effector, adenylyl cyclase, than does the wild-type allele. 相似文献
115.
We report a very rare case of an avulsion of the pectoralis major tendon in association with a two-part proximal humerus fracture. Pectoralis major tendon avulsion was confirmed intraoperatively during open reduction and internal fixation of the humerus fracture. In retrospect, the preoperative radiographic finding of posterolateral and proximal displacement of the humeral shaft suggested an injury to the pectoralis major. Because others have reported that the best treatment of a pectoralis major tendon avulsion is surgical repair, we feel that it is important to suspect such an injury in a proximal humerus fracture when this anatomic displacement is present. 相似文献
116.
Johnson Robert; Hobfoll Stevan E.; Zalcberg-Linetzy Ana 《Canadian Metallurgical Quarterly》1993,6(3):266
Examined the relationships among social support knowledge, supportive behavior, intimacy with one's spouse, and satisfaction with support provided by one's spouse among 41 Israeli kibbutz couples. The hypothesis that support knowledge and support behavior influence the intimacy between couples and increase satisfaction with spouse's social support efforts was tested. Alternative causal mechanisms are explored with simultaneous equation modeling. Results indicate that satisfaction with social support behavior by one's spouse is mediated entirely by intimacy with one's spouse. Results also indicate that partner's knowledge about social support behavior directly affects intimacy and indirectly generates social support satisfaction independent of actual supportive behavior. The findings do not differ by sex. The consistency of the findings with family behavior exchange theory and implications for marital therapy are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
117.
We show for the first time that signal processing schemes based on noncoherent signal addition will require signal transfer characteristics exhibiting high degrees of curvature. We quantify this by proposing a set of single-input, dual-output, power-conserving transfer functions and generating designs based on these characteristics. We then analyze the sensitivity of such a design scheme to nonidealities in the signal level and device behavior, and show that a sampling operation is only possible for transfer characteristics with residual "low" output of less than about 10% and low intensity reflectivity higher than 98%. For single device signal loss of up to 0.1 dB, we show that the best possible crosstalk-to-noise ratio in a packet forwarder (27 dB), is limited by the availability of the sampling operation. 相似文献
118.
Mapping of the Saccharomyces cerevisiae CDC3, CDC25, and CDC42 genes to chromosome XII by chromosome blotting and tetrad analysis 总被引:9,自引:0,他引:9
D I Johnson C W Jacobs J R Pringle L C Robinson G F Carle M V Olson 《Yeast (Chichester, England)》1987,3(4):243-253
CDC3, CDC25 and CDC42 were localized to chromosome XII by hybridizing the cloned genes to Southern blots of chromosomes separated by orthogonal-field-alternation gel electrophoresis. Meiotic tetrad analyses further localized these genes to the region distal to the RDN1 locus on the right arm of the chromosome. The STE11 gene, which had previously been mapped to chromosome XII (Chaleff and Tatchell, 1985), was found to be tightly linked to ILV5. The data suggest a map order of CEN12-RDN1-CDC42-(CDC25-CDC3)-(ILV5- STE11)-URA4. Certain oddities of the data set raise the possibility that there may be constraints on the patterns of recombination in this region of chromosome XII. 相似文献
119.
SJ Geier PA Algate K Carlberg D Flowers C Friedman B Trask LR Rohrschneider 《Canadian Metallurgical Quarterly》1997,89(6):1876-1885
The macrophage colony-stimulating factor receptor and several other hematopoietic growth factor receptors induce the tyrosine phosphorylation of a 145- to 150-kD protein in murine cells. We have previously cloned a cDNA for the murine 150-kD protein, SHIP, and found that it encodes a unique signaling intermediate that binds the SHC PTB domain through at least one tyrosine phosphorylated (NPXY) site in the carboxyl-terminal region. SHIP also contains several potential SH3 domain-binding sites, an SH2 domain for binding other tyrosine phosphorylated proteins, and an enzymatic activity that removes the phosphate from the 5 position of phosphatidylinositol 3,4,5-phosphate or from inositol 1,3,4,5-phosphate. SHIP has a negative effect on cell growth and therefore loss or modification may have profound effects on hematopoietic cell development. In this study, we have cloned a cDNA for human SHIP and examined mRNA and protein expression of SHIP and related species in bone marrow and blood cells. Flow cytometry indicates that at least 74% of immature CD34+ cells express SHIP cross-reacting protein species, whereas within the more mature population of CD33+ cells, only 10% of cells have similar expression. The majority of T cells react positively with the anti-SHIP antibodies, but significantly fewer B cells are positive. Immunoblotting detects up to seven different cross-reacting SHIP species, with peripheral blood mononuclear cells exhibiting primarily a 100-kD protein and a CD34+ acute myeloblastic leukemia expressing mainly 130-kD and 145-kD forms of SHIP. Overall, these results indicate that there is an enormous diversity in the size of SHIP or SHIP-related mRNA and protein species. Furthermore, the expression of these protein species changes according to both the developmental stage and differentiated lineage of the mature blood cell. 相似文献
120.
Combined-Stage Sintering Model 总被引:8,自引:0,他引:8
James D. Hansen Richard P. Rusin Mao-Hua Teng D. Lynn Johnson 《Journal of the American Ceramic Society》1992,75(5):1129-1135
By focusing on the similarities between the three stages of sintering, a single equation is derived that quantifies sintering as a continuous process from beginning to end. The microstructure is characterized by two separate parameters representing geometry and scale. The dimensionless geometry parameter, denoted T, comprises five scaling factors that relate specific microstructural featuers (e.g., surface curvature) to the scale (grain diameter). Calculations of T from experimental data show (a) agreement with computer simulations of initial-stage sintering, (b) the effect of surface diffusion on T, and (c) changes in T with microstructural evolution during sintering. Application of the model to the design of firing schedules and the study of microstructural geometry effects on sintering is discussed. 相似文献