全文获取类型
收费全文 | 7903篇 |
免费 | 36篇 |
专业分类
电工技术 | 16篇 |
综合类 | 2篇 |
化学工业 | 215篇 |
金属工艺 | 37篇 |
机械仪表 | 19篇 |
建筑科学 | 57篇 |
能源动力 | 33篇 |
轻工业 | 97篇 |
水利工程 | 12篇 |
石油天然气 | 1篇 |
无线电 | 119篇 |
一般工业技术 | 220篇 |
冶金工业 | 6947篇 |
原子能技术 | 16篇 |
自动化技术 | 148篇 |
出版年
2023年 | 9篇 |
2022年 | 10篇 |
2021年 | 14篇 |
2020年 | 10篇 |
2019年 | 20篇 |
2018年 | 16篇 |
2017年 | 16篇 |
2016年 | 25篇 |
2015年 | 21篇 |
2014年 | 20篇 |
2013年 | 47篇 |
2012年 | 42篇 |
2011年 | 55篇 |
2010年 | 40篇 |
2009年 | 34篇 |
2008年 | 45篇 |
2007年 | 49篇 |
2006年 | 35篇 |
2005年 | 41篇 |
2004年 | 36篇 |
2003年 | 40篇 |
2002年 | 35篇 |
2001年 | 37篇 |
2000年 | 29篇 |
1999年 | 189篇 |
1998年 | 2016篇 |
1997年 | 1199篇 |
1996年 | 803篇 |
1995年 | 431篇 |
1994年 | 388篇 |
1993年 | 437篇 |
1992年 | 68篇 |
1991年 | 113篇 |
1990年 | 127篇 |
1989年 | 111篇 |
1988年 | 120篇 |
1987年 | 104篇 |
1986年 | 92篇 |
1985年 | 69篇 |
1984年 | 13篇 |
1983年 | 24篇 |
1982年 | 46篇 |
1981年 | 58篇 |
1980年 | 66篇 |
1979年 | 11篇 |
1978年 | 31篇 |
1977年 | 192篇 |
1976年 | 380篇 |
1975年 | 26篇 |
1974年 | 10篇 |
排序方式: 共有7939条查询结果,搜索用时 0 毫秒
31.
32.
OBJECTIVE: Our purpose was to study the heterogeneity of drug response in fresh human ovarian tumors to chemotherapeutic agents in an in vitro chemosensitivity assay. STUDY DESIGN: This assay evaluates total tumor cell kill by measuring the intracellular adenosine triphosphate levels of untreated controls and drug-exposed cells at various doses after culture for 6 days. The surviving fraction is calculated by dividing the treated values with the control values. One hundred tumors were tested against four single drugs (cisplatin, the active metabolite of cytoxan, 4-hydroxyperoxy-cyclophosphamide, Taxol, and carboplatin) and two drug combinations (cisplatin plus 4-hydroxyperoxy-cyclophosphamide; cisplatin plus Taxol). RESULTS: There is great variation in the degree of cell death for single drugs and drug combinations among the 100 tumors tested. CONCLUSION: More effective clinical response to chemotherapy may be achieved in patients with ovarian cancer by selecting the most active drugs for chemotherapy, on the basis of in vitro chemosensitivity test results for individual patients. 相似文献
33.
34.
The Uniform Covering by Probabilistic Rejection (UCPR) algorithm was used, in conjunction with the Soil and Water Assessment Tool (SWAT) model, to identify P loads from point source and nonpoint source polluters in the upper Etowah River basin (UERB) in Georgia. The key findings of the research are as follows. The mean absolute error was preferred over the root mean square error as a search criterion for the UCPR algorithm when water quality observations are scarce. The undocumented P load from point sources in the UERB was consistently estimated as about 43 kg/d by the proposed method; but the method was not able to identify the broiler litter application rate to the poultry/beef operation pastures. Point sources (both documented and undocumented), poultry/beef operation pastures, and forests are the three major contributors of P. During 1992-1996, on average they accounted for 36.4, 31.7, and 17.2% of P load from the UERB, respectively. 相似文献
35.
36.
37.
38.
39.
YL Liu SJ Riederer PJ Rossman RC Grimm JP Debbins RL Ehman 《Canadian Metallurgical Quarterly》1993,30(4):507-511
OBJECTIVE: To evaluate the diagnostic accuracy and clinical usefulness of high-resolution transvaginal duplex Doppler ultrasound in postpartum and post-abortion patients with excessive hemorrhage who are suspected of having residual trophoblast. METHODS: Forty-eight women with excessive hemorrhage referred for possible residual trophoblastic tissue were evaluated by transvaginal duplex Doppler ultrasonography. Based on two-dimensional imaging, the patients were divided prospectively into groups: women who had an empty uterus with a normal uterine cavity, those with a pure endometrial fluid collection and no echogenic foci, those who had a mixed endometrial fluid collection with foci of echogenicity, and those with intracavitary heterogeneous material with mixed echo patterns of fluid and solid components. In each group, Doppler studies were performed and the resistance index (RI) was calculated. The two-dimensional patterns and Doppler results were correlated with clinical and pathologic follow-up. RESULTS: Twenty-eight subjects had a normal uterine cavity and seven had a pure endometrial fluid collection; all were treated conservatively and none showed later clinical evidence of residual trophoblastic tissue. In 13 women, residual trophoblast was strongly suggested from the images of two-dimensional ultrasonography: Five showed an endometrial fluid collection with some echogenic foci, and eight exhibited intracavitary mixed echogenic material. All underwent curettage, and residual trophoblastic tissue was found in ten of the 13. The mean (+/- standard deviation) RI to flow in the myometrial arteries was 0.54 +/- 0.15 in women without residual trophoblast and 0.35 +/- 0.1 in those with residual trophoblastic tissue (P < .01). CONCLUSION: Our experience suggests that transvaginal duplex Doppler ultrasonography is an effective noninvasive method for evaluating patients with excessive postpartum and post-abortion hemorrhage who are suspected of having residual trophoblastic tissue. Its use enhances the positive preoperative diagnosis of residual trophoblastic tissue and may reduce unnecessary curettage procedures. 相似文献
40.
JJ Callaghan GS Tooma JP Olejniczak DD Goetz RC Johnston 《Canadian Metallurgical Quarterly》1996,(333):118-125
The senior authors' initial experience with primary hybrid hip replacement in patients with osteoarthritis was studied to evaluate the efficacy of the procedure. Hybrid total hip arthroplasty (uncemented Harris-Galante acetabular component and cemented Iowa precoated femoral component) was performed in 131 consecutive, nonselected hips in 118 patients with the diagnosis of primary osteoarthritis. Followup was performed at 8 to 9 years after the procedure. The average age at the time of the procedure was 68 years (range, 45-87 years). There were 50 men (55 hips) and 68 women (76 hips). At final followup 19 patients (22 hips) had died. The femoral component had been revised for aseptic loosening in 8 hips (6.1%). One additional hip showed definite radiographic loosening. Hence, the prevalence of radiographic femoral failure was 6.9% (9 hips). No acetabular component had been revised for aseptic loosening and no acetabular component had migrated. The senior author continues to perform hybrid total hip arthroplasty in all patients with primary osteoarthritis. However, design modifications have been made in the femoral component that is used. 相似文献