全文获取类型
收费全文 | 2997篇 |
免费 | 86篇 |
国内免费 | 34篇 |
专业分类
电工技术 | 55篇 |
综合类 | 38篇 |
化学工业 | 262篇 |
金属工艺 | 112篇 |
机械仪表 | 43篇 |
建筑科学 | 72篇 |
矿业工程 | 9篇 |
能源动力 | 48篇 |
轻工业 | 164篇 |
水利工程 | 27篇 |
石油天然气 | 12篇 |
武器工业 | 7篇 |
无线电 | 106篇 |
一般工业技术 | 215篇 |
冶金工业 | 1780篇 |
原子能技术 | 34篇 |
自动化技术 | 133篇 |
出版年
2023年 | 8篇 |
2022年 | 13篇 |
2021年 | 18篇 |
2020年 | 17篇 |
2019年 | 25篇 |
2018年 | 30篇 |
2017年 | 27篇 |
2016年 | 36篇 |
2015年 | 17篇 |
2014年 | 32篇 |
2013年 | 66篇 |
2012年 | 64篇 |
2011年 | 112篇 |
2010年 | 83篇 |
2009年 | 77篇 |
2008年 | 97篇 |
2007年 | 79篇 |
2006年 | 58篇 |
2005年 | 65篇 |
2004年 | 52篇 |
2003年 | 28篇 |
2002年 | 34篇 |
2001年 | 32篇 |
2000年 | 36篇 |
1999年 | 59篇 |
1998年 | 534篇 |
1997年 | 309篇 |
1996年 | 197篇 |
1995年 | 134篇 |
1994年 | 108篇 |
1993年 | 99篇 |
1992年 | 24篇 |
1991年 | 23篇 |
1990年 | 31篇 |
1989年 | 37篇 |
1988年 | 38篇 |
1987年 | 27篇 |
1986年 | 21篇 |
1985年 | 28篇 |
1984年 | 7篇 |
1983年 | 10篇 |
1982年 | 15篇 |
1981年 | 18篇 |
1980年 | 22篇 |
1979年 | 13篇 |
1978年 | 9篇 |
1977年 | 65篇 |
1976年 | 129篇 |
1971年 | 6篇 |
1967年 | 10篇 |
排序方式: 共有3117条查询结果,搜索用时 15 毫秒
961.
进行了粗、细集料不同类型组合、不同成型压力、不同旋转压实次数比较等试验,研究了辉绿岩作为高速公路沥青表面层的可行性. 相似文献
962.
在对2:17稀土-过渡族化合物的研究中经常要由高温外推出低温顺磁态下物质晶胞参数和单胞体积的变化趋势,并绘制出热膨胀曲线。因此利用VC++语言编写了“2:17型稀土-过渡族化合物顺磁态热膨胀曲线的计算程序”以高效精确完成此工作。 相似文献
963.
964.
BP Meij G Voorhout TS van den Ingh HA Hazewinkel E Teske A Rijnberk 《Canadian Metallurgical Quarterly》1998,27(3):246-261
OBJECTIVE: To evaluate microsurgical transsphenoidal hypophysectomy in dogs with pituitary-dependent hyperadrenocorticism (PDH). STUDY DESIGN: Prospective study to evaluate the results (survival and disease-free interval, remission, recurrence) and complications of microsurgical transsphenoidal hypophysectomy by clinical follow-up, computed tomography (CT), and urinary corticoid-to-creatinine (C/C) ratios in dogs with PDH. The effect of surgical experience was investigated by comparing results of hypophysectomy cases 1 through 26 and 27 through 52. ANIMALS OR SAMPLE POPULATION: 52 dogs with PDH. RESULTS: Preoperative CT enabled accurate assessment of pituitary size (24 nonenlarged and 28 enlarged) and localization relative to intraoperative anatomic landmarks. Treatment failures included procedure-related mortalities (five dogs) and incomplete hypophysectomies (four dogs). The 1-year estimated survival rate was 84% (95% confidence interval [CI], 71% to 92%). The 2-year estimated survival rate was 80% (95% CI, 65% to 90%). In 43 dogs, the hyperadrenocorticism went into remission. Hyperadrenocorticism recurred in five dogs. The 1-year estimated relapse-free fraction was 92% (95% CI, 76% to 97%). The main complications were transient, mild, postoperative hypernatremia; transient reduction or cessation of tear production (25 eyes in 18 dogs); permanent (five dogs) or prolonged (nine dogs) diabetes insipidus; and secondary hypothyroidism. Normal tear production had resumed in all but one case after a median period of 10 weeks. In the second case series (27 through 52), the hospitalization period was shorter, the number of dry eyes fewer, the survival fraction greater, and the postoperative mortality lower than in the first series. In 15 dogs in which remission was obtained, postoperative CT images suggested the presence of small pituitary remnants; in 1 of these, hyperadrenocorticism recurred. In 46 dogs, the histological diagnosis was pituitary adenoma. CONCLUSIONS: Microsurgical transsphenoidal hypophysectomy in dogs with PDH is an effective method of treatment in specialized veterinary institutions having access to advanced pituitary imaging techniques. Postoperative CT findings do not correlate well with remission or subsequent recurrence of hyperadrenocorticism. CLINICAL RELEVANCE: The neurosurgeon performing hypophysectomies must master a learning curve and must be familiar with the most frequent complications of the operation to recognize them as early as possible and to treat them immediately and effectively. Urinary C/C ratios are sensitive indicators for the assessment of remission and recurrence of hyperadrenocorticism. 相似文献
965.
MC Deng M Erren N Roeder V Dreimann F Günther S Kerber HA Baba C Schmidt G Breithardt HH Scheld 《Canadian Metallurgical Quarterly》1998,65(9):1255-1261
BACKGROUND: In the early period after cardiac transplantation, differential diagnosis of graft failure due to rejection, infection, and other causes is important but difficult. METHODS: In 22 consecutive patients undergoing heart transplantation, we prospectively determined levels of interleukin-6 as well as T-cell and monocyte subsets at eight points in time during biopsy and right heart catheterization and within 12 hr of echocardiography during the first 3 months after transplantation. RESULTS: Worse hemodynamic parameters, as characterized by dichotomization according to median values (pulmonary capillary wedge pressure >10 mmHg, mean pulmonary arterial pressure > 18 mmHg, pulmonary vascular resistance > 115 dyn x sec x cm(-5), right atrial pressure > 5 mmHg, cardiac index <3 L/min/m2, early mitral deceleration time < 135 msec, and isovolumic relaxation time <80 msec), were associated with higher levels of interleukin-6, C-reactive protein, polymorphonuclear cells, CD71+/CD14+ monocytes, and IgM levels and, in contrast, with lower levels of immunocompetence markers such as CD3+ T cells, CD4+ T cells, CD8+ T cells, CD3+/CD25+ T cells, CD4+/ CD45RO+ T cells, NK cells, and lower biopsy scores. CONCLUSION: Early after cardiac transplantation, elevated levels of inflammatory cells and soluble inflammatory molecules and lower levels of immunocompetence markers are associated with impaired allograft function in the absence of cellular rejection. 相似文献
966.
Willi?Geiselmann Willi?Meier Rainer?SteinwandtEmail author 《International Journal of Information Security》2003,2(1):59-64
As a possible new mathematical basis for authentication and signature schemes, at EUROCRYPT 96 J. Patarin introduced the isomorphisms of polynomials (IP) problem [4, 5]. In this contribution, we describe an attack on the secret key of IP with one secret and demonstrate its efficiency through examples with realistic parameter sizes. The attack is carried out by means of a computer algebra system on ordinary PCs. Finally, we give a brief discussion of limits of our attack that points out possible directions for solving the mentioned security problems. 相似文献
967.
对测量阻抗型和相量比较型两种类型的电抗距离继电器的抗稳态超越的能力进行了研究,主要包括负荷的影响和同相问题的研究.同时,构造了一个新的电抗型距离继电器判据和算法,该算法具有方向性,且不受负荷和同相问题的影响,解决了由于负荷和同相问题引起的稳态超越现象,提高了保护动作的可靠性.电磁暂态仿真结果证明该原理具有防止负荷和同相问题引起的稳态超越和保护范围不足的问题. 相似文献
968.
969.
970.
A large amount of static and dynamic NMR experiments have been carried out to determine the spin properties in high temperature superconductors cuprates (HTSC). In the majority of cuprates the magnetic shift at the planar copper nucleus is independent of the temperature when the field is applied perpendicular to the CuO2 planes and does not exhibit the expected reduction of the spin susceptibility in the superconducting state. This has been explained by a coincidental cancellation of on-site and transferred hyperfine fields at the copper nucleus, which would lead to a vanishing spin shift. To examine this explanation we determine the hyperfine fields by ab initio cluster calculations for La2CuO4 within the framework of spin-polarized density functional theory. In particular we investigate the sensitivity of the hyperfine fields on the lattice constants. 相似文献