全文获取类型
收费全文 | 16314篇 |
免费 | 349篇 |
国内免费 | 210篇 |
学科分类
工业技术 | 16873篇 |
出版年
2023年 | 64篇 |
2022年 | 145篇 |
2021年 | 236篇 |
2020年 | 154篇 |
2019年 | 163篇 |
2018年 | 250篇 |
2017年 | 248篇 |
2016年 | 263篇 |
2015年 | 206篇 |
2014年 | 287篇 |
2013年 | 495篇 |
2012年 | 434篇 |
2011年 | 591篇 |
2010年 | 471篇 |
2009年 | 447篇 |
2008年 | 445篇 |
2007年 | 351篇 |
2006年 | 388篇 |
2005年 | 338篇 |
2004年 | 288篇 |
2003年 | 300篇 |
2002年 | 309篇 |
2001年 | 236篇 |
2000年 | 207篇 |
1999年 | 355篇 |
1998年 | 2193篇 |
1997年 | 1382篇 |
1996年 | 924篇 |
1995年 | 547篇 |
1994年 | 517篇 |
1993年 | 567篇 |
1992年 | 158篇 |
1991年 | 162篇 |
1990年 | 211篇 |
1989年 | 203篇 |
1988年 | 186篇 |
1987年 | 166篇 |
1986年 | 156篇 |
1985年 | 137篇 |
1984年 | 63篇 |
1983年 | 74篇 |
1982年 | 70篇 |
1981年 | 122篇 |
1980年 | 76篇 |
1979年 | 56篇 |
1978年 | 73篇 |
1977年 | 228篇 |
1976年 | 406篇 |
1975年 | 58篇 |
1971年 | 89篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
1.
Kurjenniemi Janne Hämäläinen Seppo Ristaniemi Tapani 《Wireless Personal Communications》2003,27(4):337-351
In this article we consider the performance of the 3.84 Mcpstime-division duplex (TDD) mode of UTRA (Universal TerrestrialRadio Access) network. We emphasize two of the radio resourcemanagement algorithms, handover and uplink power control, whoserole in the overall system performance is studied extensively.First, a handover algorithm used in WCDMA (Wideband Code DivisionMultiple Access) standard is considered in a TDD-mode operation.This gives rise to a careful setting of different handoverparameters, and the evaluation of the effects to the systemperformance. Secondly, the specified uplink power controlalgorithm is considered. Since it is based on several user-mademeasurements which may involve both random and systematic errors acareful study about the suitability of the power control scheme iscarried out. 相似文献
2.
No authorship indicated 《Canadian Metallurgical Quarterly》2004,59(8):673
Provides the biography of Sheldon Cohen and announces that he has received the APA Award for Distinguished Scientific Contributions (2004) for his elegant research in psychoneuroimmunology. The award citation and a selected bibliography are also provided. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
3.
量子密码技术被认为是绝对安全的加密技术。近年来,在美国、德国、日本和中国,相关研究都取得了明显进展。2004年6月,世界上第一个量子密码通信网络在美国马萨诸塞州剑桥城正式投入运行,标志着这一技术迈上了新台阶。据相关机构估算,量子保密通信系统一旦商用,将形成高达10亿美元的市场。 相似文献
4.
No authorship indicated 《Canadian Metallurgical Quarterly》1997,52(8):912
Presents a list of American Psychological Foundation contributors for 1996. Individuals listed have donated through gifts of cash, securities, royalties, or through the Legacy Club (LC). LC donations are provided in wills, life insurance policies, trusts, and other gift arrangements. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
5.
Assuming that the chemical reactions used to synthesize a combinatorial library member are successful, then knowledge of the specific reaction sequence is equivalent to knowing the member's chemical identity. Because the determination of chemical identity is typically not automatable and requires a substantial amount of material, schemes that encode a member's reaction history onto the reaction platform are of value. The primary benefits of encoding are relational nomenclature (all methods) and automated handling (some methods). Encoding methods evaluated to date are spatial, graphical, chemical, spectrometric, electronic, and physical. 相似文献
6.
OBJECTIVES: To assess that neuromuscular relaxation onset of the adductor pollicis (AP) is related to neuromuscular stimulation rate. To assess that train-of-four (TOF) at 0.05 Hz is a more accurate indicator of optimal tracheal intubation time and conditions, than TOF at 0.08 Hz. STUDY DESIGN: Prospective, comparative, randomized double-blind study. PATIENTS: Forty adults, physical class ASA 1 or 2, undergoing general anaesthesia with tracheal intubation were allocated to two groups (n = 20) according to the sequence of stimulation of the AP: either TOF at 0.05 Hz (test group) or TOF at 0.08 Hz (control group). METHODS: Induction of anaesthesia was achieved with thiopentone, fentanyl and vecuronium (0.1 mg.kg-1). Neuromuscular monitoring was obtained with force displacement transducers attached to each AP. Tracheal intubation was performed once AP muscular response obtained with TOF at 0.05 Hz for test group and TOF at 0.08 Hz for control group was abolished. Results are expressed as mean +/- SEM. Fisher exact test was used for intubation conditions comparison. Curarization time between groups was compared with unpaired Student's t test (P < 0.05 accepted). RESULTS: TOF with 0.05 Hz stimulation significantly increased curarization time: 217 +/- 7 versus 162 +/- 6 s (P < 0.001). Intubation conditions were excellent in 95% and good in 5% of patients in the study group, compared to 15 and 40% in the control group, respectively (P < 0.01) in 45% of the control group patients coughing at intubation occurred. CONCLUSION: Low stimulation rate (TOF at 0.05 Hz) of AP is a reliable technique to determine the appropriate intubation time for patients paralyzed with vecuronium. 相似文献
7.
钻井液用BDY-1便携式堵漏仪 总被引:3,自引:2,他引:1
在堵漏过程中,对堵漏材料和堵漏浆配方的优选是决定堵漏成功的关键。为了能在现场对堵漏进行评价,研制出BDY-1便携式堵漏仪,该堵漏仪主要由不锈钢钢柱圈钢,压力表等加工而成,该堵漏仪体积小,重量轻,价格低,仅为国产堵漏仪的1/20。试验结果表明BDY-1便携式堵漏仪操作简便,可快速对堵漏材料进行评价并筛选出堵漏配方;数据重复性好,准确可靠,能达到进口或国产堵漏仪的水平;在模拟漏层选定后,可采用多套压力梯度,对堵漏浆封堵效果进行评价,在压力梯度选定后,可评价堵漏浆对不同类型漏层的封堵效果;如果扩大压力范围,可对封堵后的漏层进行破裂试验,从而确定合理的钻井施工参数;适用现场操作和应用。 相似文献
8.
茅金根 ,梁秀文 ,杨午阳 ,冯有奎 .等偏移距自动初至静校正 .石油地球物理勘探 ,2 0 0 2 ,37(5 ) :4 6 9~ 4 72 本文提出一种自动计算静校正量的新方法。它首先在等偏移距道集内对相邻道的初至波采用高精度相关构建一个关于炮、检时差的超大矩阵方程 ,然后采用优化统计迭代算法求解炮点和检波点的静校正量 ,并用概率分布函数确定精确的炮、检静校正量 ,最后用误差校正函数消除炮、检静校正误差。实际资料处理结果表明 ,本方法自动、省时、精度高。 相似文献
9.
Summary The influence of draw ratio on macroscopic and crystallographic density of polyethylene with different initial morphologies, has been investigated by solid-state extrusion. An initial drop followed by an increase in macroscopic density as a function of draw ratio has been observed. Since precision X-ray measurements of unit cell parameters showed no variation of crystallographic density, it was concluded that plastic deformation of polyethylene upon drawing proceeds with a decrease of the degree of crystallinity. This was confirmed by differential scanning calorimetry. 相似文献
10.