全文获取类型
收费全文 | 2191篇 |
免费 | 1篇 |
专业分类
电工技术 | 1篇 |
化学工业 | 39篇 |
金属工艺 | 2篇 |
机械仪表 | 4篇 |
建筑科学 | 4篇 |
能源动力 | 2篇 |
轻工业 | 1篇 |
水利工程 | 1篇 |
无线电 | 4篇 |
一般工业技术 | 20篇 |
冶金工业 | 2100篇 |
自动化技术 | 14篇 |
出版年
2024年 | 1篇 |
2021年 | 1篇 |
2020年 | 4篇 |
2019年 | 1篇 |
2018年 | 1篇 |
2017年 | 1篇 |
2015年 | 3篇 |
2014年 | 2篇 |
2013年 | 8篇 |
2012年 | 9篇 |
2011年 | 2篇 |
2010年 | 5篇 |
2009年 | 3篇 |
2008年 | 3篇 |
2007年 | 3篇 |
2006年 | 1篇 |
2005年 | 2篇 |
2004年 | 7篇 |
2003年 | 11篇 |
2002年 | 1篇 |
2001年 | 1篇 |
2000年 | 3篇 |
1999年 | 89篇 |
1998年 | 683篇 |
1997年 | 354篇 |
1996年 | 256篇 |
1995年 | 131篇 |
1994年 | 117篇 |
1993年 | 141篇 |
1992年 | 15篇 |
1991年 | 22篇 |
1990年 | 26篇 |
1989年 | 20篇 |
1988年 | 25篇 |
1987年 | 10篇 |
1986年 | 14篇 |
1985年 | 14篇 |
1983年 | 6篇 |
1982年 | 8篇 |
1981年 | 7篇 |
1980年 | 17篇 |
1979年 | 2篇 |
1978年 | 6篇 |
1977年 | 43篇 |
1976年 | 109篇 |
1975年 | 1篇 |
1973年 | 1篇 |
1966年 | 1篇 |
1955年 | 1篇 |
排序方式: 共有2192条查询结果,搜索用时 0 毫秒
91.
OBJECTIVE: To determine the relationship between sperm motility and sperm morphology parameters and IVF and pregnancy rates. DESIGN: Pre- and postpreparation analysis of semen samples from infertile couples undergoing IVF-ET. SETTING: Andrology Laboratory, Royal Maternity Hospital, Belfast, Northern Ireland. PATIENT(S): One hundred fifty couples undergoing IVF-ET treatment at the Regional Fertility Centre. INTERVENTION(S): None. MAIN OUTCOME MEASURE(S): The ability of human sperm to achieve IVF and pregnancy was investigated in relation to motility parameters (assessed with computer-aided sperm analysis [Integrated Visual Optical System] and percent normal morphology (determined with the strict criteria). RESULT(S): Significant differences were observed in motility parameters and percent normal morphology in samples that achieved > or =50% fertilization compared with < or =50% fertilization and between samples that achieved a pregnancy compared with those that did not. Significant positive correlations were observed between percent progressive motility, the velocity of sperm movement, and morphology parameters and both IVF and pregnancy. CONCLUSION(S): Both sperm motility parameters and percent normal morphology are significant factors in predicting fertilization and pregnancy rates in IVF. 相似文献
92.
HR Shinefield SB Black BO Staehle T Adelman K Ensor A Ngai CJ White SR Bird H Matthews BJ Kuter 《Canadian Metallurgical Quarterly》1998,17(11):980-985
OBJECTIVES AND STUDY DESIGN: The primary objectives of this study were to compare immunologic responses, antibody persistence, safety and varicella breakthrough rates when VARIVAX (varicella vaccine) is given at the same time as M-M-R II (measles, mumps, rubella vaccine) and TETRAMUNE (conjugate Haemophilus influenzae type b, diphtheria, tetanus and whole cell pertussis vaccine) at separate injection sites (Group A) vs. VARIVAX given 6 weeks after M-M-R II and TETRAMUNE (Group B). Six hundred nine healthy children, 12 to 23 months of age, were randomized to one of two treatment (immunization) groups (Group A and Group B). Blood for antibody titers was drawn on the day of immunization, 6 weeks after each injection and 1 year later. Local and systemic adverse reactions were recorded. Exposure and cases of varicella were documented through a 1-year follow-up period. RESULTS: Measles, mumps and rubella seroconversion rates and geometric mean titers (GMTs) were similar for both treatment groups. Varicella seroconversion rates were also similar between groups. However, varicella GMTs and percent with a varicella-protective level [> or =5.0 glycoprotein (gp) enzyme-linked immunosorbent assay (ELISA) units] did not meet the prespecified criteria for similarity were lower for Group A (GMT 10.5; 82.8% > or =5.0 gp ELISA units) than for Group B (GMT 14.5; 91.2% > or =5.0 gp ELISA units). The GMTs between groups for other antibodies were similar. At the 1-year follow-up antibody titers were comparable in both groups and breakthrough varicella cases appeared generally similar. There were fewer local adverse events (AEs) at the VARIVAX injection sites (9.8% and 2.9%, Group A and B, respectively) than at the TETRAMUNE sites (27.9% and 24.0%). Systemic AEs were not statistically different when M-M-R II was administered alone (8.6%) or concomitantly with VARIVAX (8.9%). When VARIVAX was given alone AEs were 1.8%. The rate of fever > or =102 degrees F after M-M-R II and TETRAMUNE administered together was 10.7% on Days 0 to 3 and 23.7% on Days 7 to 21. When VARIVAX was administered alone, the rate of fever was 5.4% on Days 0 to 3 (P = 0.018) and 10.8% on Days 7 to 21 (P<0.001). CONCLUSION: Because the varicella titers were comparable and varicella breakthrough rates generally similar at 1 year in both groups, we expect that the concomitant administration of VARIVAX with M-M-R II and TETRAMUNE has clinical effectiveness similar to that with VARIVAX 6 weeks after the administration of these other two vaccines. VARIVAX appears to be less reactogenic than M-M-R II and TETRAMUNE. 相似文献
93.
94.
95.
Complementary DNA was synthesized using polyadenylated nuclear RNA of cultured Drosophila cells as template. The kinetics of hybridization of this cDNA with nuclear RNA indicated that the complexity of this RNA population is five to ten times greater than that of cytoplasmic mRNA. The same difference in the fraction of DNA represented was obtained when nuclear and cytoplasmic RNA were hybridized with labeled unique sequence DNA. The fraction of the DNA sequences represented in total number of polyadenylated nuclear RNA is much higher than that represented in cytoplasmic RNA. 相似文献
96.
97.
98.
99.
A simple, heuristic model of a photographic emulsion is described for the purpose of illustrating the fundamental physical processes and emulsion properties which determine the characteristics of an x-ray film (viz., the shape of the H - D curve, film gamma, and film speed). By means of this model, it is shown that the contrast multiplication afforded by an x-ray film (i.e., a film gamma greater than unity) is a direct result of the exponential attenuation of the viewing light by the developed film, and that film gamma is proportional to grain size, grain density, and emulsion thickness. The difference in the H - D curve that is observed when the same film is exposed to light from an intensifying screen or directly to x rays is also predicted by the model. 相似文献
100.
The nonapeptide oxytocin (OT) is important for uterine contractility at parturition, milk ejection during lactation, and the induction of maternal behavior. OT messenger ribonucleic acid (mRNA) levels increase in the paraventricular and supraoptic nuclei (PVN and SON) of late pregnant and lactating rats and are modulated by the steroid milieu that accompanies these states. Specifically, sequential exposure to estradiol (E2) and progesterone (P) followed by P withdrawal 48 hrs prior to sacrifice increases PVN, and to a lesser but significant degree, SON OT mRNA. To better define the time course of induction of OT mRNA levels following P withdrawal, ovariectomized Sprague-Dawley rats were treated with empty or steroid-filled capsules. On day 1, animals received an E2-filled or empty capsule, followed by P-filled or empty capsules on day 3. On day 14, P-filled or empty capsules were removed and animals were sacrificed 24, 36, or 48 hrs later. The hypothalamic PVN were analyzed for OT mRNA by in situ hybridization histochemistry. Significant differences in PVN OT mRNA were found among the groups (P<0.0001, Kruskal-Wallis). Animals in the 48 hr (P=0.007) and 36 hr (P=0.005), but not the 24 hr, steroid-treated groups had significantly increased OT mRNA relative to their respective sham-treated cohorts (Mann-Whitney U test). The relative abundance of PVN OT mRNA differed among the steroid-treated groups (Kruskal-Wallis, P<0.0003), with highest levels at 48 hr. We conclude that increases in PVN OT mRNA occur by 36 hrs, and are highest at 48 hrs, after P withdrawal in the E2-primed rat. Future studies will determine if OT-mediated changes in behavior or physiology that surround parturition are related to these changes in OT mRNA. 相似文献