全文获取类型
收费全文 | 54568篇 |
免费 | 5150篇 |
国内免费 | 3178篇 |
专业分类
电工技术 | 3335篇 |
技术理论 | 3篇 |
综合类 | 4347篇 |
化学工业 | 8259篇 |
金属工艺 | 2864篇 |
机械仪表 | 2873篇 |
建筑科学 | 4459篇 |
矿业工程 | 1476篇 |
能源动力 | 1599篇 |
轻工业 | 3977篇 |
水利工程 | 1031篇 |
石油天然气 | 2559篇 |
武器工业 | 360篇 |
无线电 | 5955篇 |
一般工业技术 | 5663篇 |
冶金工业 | 5804篇 |
原子能技术 | 700篇 |
自动化技术 | 7632篇 |
出版年
2024年 | 213篇 |
2023年 | 907篇 |
2022年 | 1532篇 |
2021年 | 2207篇 |
2020年 | 1694篇 |
2019年 | 1636篇 |
2018年 | 1655篇 |
2017年 | 1787篇 |
2016年 | 1501篇 |
2015年 | 2119篇 |
2014年 | 2535篇 |
2013年 | 2948篇 |
2012年 | 3111篇 |
2011年 | 3253篇 |
2010年 | 3045篇 |
2009年 | 2800篇 |
2008年 | 2757篇 |
2007年 | 2575篇 |
2006年 | 2512篇 |
2005年 | 2055篇 |
2004年 | 1825篇 |
2003年 | 2357篇 |
2002年 | 3223篇 |
2001年 | 2690篇 |
2000年 | 1444篇 |
1999年 | 1228篇 |
1998年 | 1715篇 |
1997年 | 1168篇 |
1996年 | 1008篇 |
1995年 | 683篇 |
1994年 | 555篇 |
1993年 | 488篇 |
1992年 | 246篇 |
1991年 | 181篇 |
1990年 | 176篇 |
1989年 | 173篇 |
1988年 | 112篇 |
1987年 | 105篇 |
1986年 | 83篇 |
1985年 | 90篇 |
1984年 | 23篇 |
1983年 | 16篇 |
1982年 | 31篇 |
1981年 | 25篇 |
1980年 | 48篇 |
1979年 | 8篇 |
1978年 | 7篇 |
1977年 | 88篇 |
1976年 | 237篇 |
1975年 | 7篇 |
排序方式: 共有10000条查询结果,搜索用时 176 毫秒
71.
72.
JJ Harris DK Lunt SB Smith WL Mies DS Hale M Koohmaraie JW Savell 《Canadian Metallurgical Quarterly》1997,75(4):986-992
Two groups of Brangus steers produced by nuclear transplantation cloning were used in parallel studies investigating the impact of calf- and yearling-feeding. The first group (n = 8) were fed as calves (CF; n = 4) or yearlings (YF; n = 4) to a constant age end point of 16 mo. The second group (n = 10) were fed as calves (CF; n = 5) or yearlings (YF; n = 5) to a constant live weight end point (530 kg). When slaughtered at the same age, CF and YF steers did not differ (P > .05) in feedlot ADG, but the CF steers were heavier and had higher dressing percentages, numeric yield grades, and quality grades (P < .05). Top loin steaks from the groups of steers did not differ (P > .05) in palatability traits. When fed to a constant live weight, the YF steers gained more rapidly (P < .05) and had lower (P < .05) numeric yield grades than did CF steers. Again CF steers had higher (P < .05) dressing percentages. There was no difference (P > .05) between the treatments in carcass quality grade or meat palatability characteristics. Thus, when finished to a constant weight end point, YF steers gained more rapidly, with no adverse effects on carcass quality grade or palatability traits; however, CF steers consistently produced higher dressing percentages, largely due to greater external fatness. 相似文献
73.
JW Rhee 《The Journal of communication》1997,47(3):26-48
This study examines how news frames in campaign coverage affect individuals' interpretation of campaigns. Framing effects are conceptualized in terms of the process by which textual features in news stories set limits on knowledge use in the construction of a discourse model - a mental model constructed through the interaction between news frames and the interpreter's social knowledge. Examining message structures in campaign news stories led to identifying two major frames in campaign coverage: strategy and issue. Narrative data collected from two field experiments were analyzed. The findings suggest that both strategy-framed and issue-framed print news stories are effective in influencing campaign interpretation. 相似文献
74.
Vertical phoria (vertical vergence in the absence of binocular feedback) can be trained to vary with non-visual cues such as vertical conjugate eye position, horizontal conjugate eye position and horizontal vergence. These prior studies demonstrated a low-level association or coupling between vertical vergence and several oculomotor cues. As a test of the potential independence of multiple eye-position cues for vertical vergence, context-specific adaptation experiments were conducted in three orthogonal adapting planes (midsagittal, frontoparallel, and transverse). Four vertical disparities in each of these planes were associated with various combinations of two specific components of eye position. Vertical disparities in the plane were associated with horizontal vergence and vertical conjugate eye position; vertical disparities in the frontoparallel plane were associated with horizontal and vertical conjugate eye position; and vertical disparities in the transverse plane were associated with horizontal vergence and horizontal conjugate eye position. The results demonstrate that vertical vergence can be adapted to respond to specific combinations of two different sources of eye-position information. The results are modeled with an association matrix whose inputs are two classes of eye position and whose weighted output is vertical vergence. 相似文献
75.
BM Chen LY Chan SM Wang MF Wu JW Chern SR Roffler 《Canadian Metallurgical Quarterly》1997,73(3):392-402
We examined the in vivo efficacy of targeting beta-glucuronidase (betaG) to activate a glucuronide prodrug (BHAMG) of p-hydroxyaniline mustard (pHAM) at hepatoma ascites in Sprague-Dawley rats. Injection i.p. of 500 microg RH1-betaG, a conjugate formed between recombinant betaG and monoclonal antibody RH1 with specificity for an antigen expressed on AS-30D rat hepatoma cells, into rats bearing AS-30D ascites resulted in the accumulation of 54 microg conjugate per 10(9) tumor cells after 2 hr. Ascites fluid and serum contained 0.53 and 0 microg/ml, respectively, RH1-betaG 2 hr after injection of the conjugate. Conjugate binding to AS-30D cells was heterogeneous and non-saturated, as determined by flow cytometry. BHAMG was less toxic than pHAM to SD rats based on measures of animal mortality, weight loss and hematological toxicity. Treatment of rats bearing established hepatoma ascites with 500 microg RH1-betaG followed 2 hr later with a single i.p. injection of 30 mg/kg BHAMG or 3 i.p. injections of 10 mg/kg BHAMG 2, 3 and 4 hr later resulted in the cure of 6/8 and 8/8 animals, respectively. Treatment with BHAMG or pHAM alone did not produce cures, whereas treatment with a control antibody-betaG conjugate and BHAMG produced significantly greater hematological toxicity compared to treatment with RH1-betaG and BHAMG. All cured rats were completely protected from rechallenge with 2 x 10(7) AS-30D cells, indicating that successful treatment of animals induced protective immunity. 相似文献
76.
本文用计算机数字模拟方法研究了电活性分子多层Z型L-B膜修饰电极的循环伏安行为。计算了电极与修饰L-B膜分子第一层之间的电荷转移速度常数K_o,L-B膜分子层间的电荷转移速度常数k_i;对峰电位差△E_p及阳极峰面积Q的影响,以及在不同条件下各层分子的氧化态分数随扫描时间的变化。为研究和设计电活性分子修饰电极的实际体系提供了大量数据和信息。 相似文献
77.
78.
Sensory activity mediates regulation of tyrosine hydroxylase (TH), the first enzyme in the dopamine biosynthetic pathway, in the rodent olfactory bulb. The current studies established for the first time primary cultures of neonatal mouse olfactory bulb expressing TH and tested whether L-type calcium channels mediate the activity-dependent regulation of the dopamine phenotype. After 1 d in vitro (DIV), a small population of TH-immunostained neurons that lacked extensive processes could be demonstrated. After an additional 2 DIV in serum-free medium, the number of TH neurons had doubled, and they exhibited long interdigitating processes. Membrane depolarization for 48 hr with 50 mM KCl produced a further 2.4-fold increase in the number of TH-immunoreactive neurons compared with control cultures. Increased TH neuron number required at least 36 hr of exposure to KCl. Forskolin, which increases intracellular cAMP levels, induced a 1.5- to 1.6-fold increase in the number of TH-immunostained neurons. Combined treatment with KCl and forskolin was not additive. Nifedipine, an L-type calcium channel blocker, completely prevented the depolarization-mediated increase in TH expression but did not block the response to forskolin. Treatment with Bay K8644, an L-type calcium channel agonist, also significantly increased the number of TH-expressing neurons. Depolarization also induced alterations in neuritic outgrowth, resulting in a stellate versus an elongate morphology that, in contrast, was not prevented by nifedipine. These results are the first demonstration that in vitro, as in vivo, depolarization increases TH expression in olfactory bulb and that L-type calcium channels mediate this activity-dependent regulation of the dopamine phenotype. 相似文献
79.
80.
印刷质量控制的基本方法(一)综述 总被引:1,自引:0,他引:1
无论哪一种印刷品的生产都要经过若干个工艺过程,才能将原稿上的图文信息转移到承印物上。由于印刷技术的飞跃发展,标准化和质量控制成为一个很重要的问题。标准化和质量控制在很大程度上是依靠仪器和控制装置来实现的。科学技术的极大发展,大大地推动了印刷技术的发展,印刷所使用的原材料和工艺得到了很大的改进,逐步实现了标准化,提高并稳定了生产高质量产品的能力。目前我们评价印刷品质量的优劣大致有三种方法:主观评价法、客观评价法和综合评价法。主观评价法,是以原稿为基础对照样张来评价。这里有人为的因素,根据评价人的知… 相似文献