全文获取类型
收费全文 | 4144篇 |
免费 | 259篇 |
国内免费 | 76篇 |
专业分类
电工技术 | 183篇 |
综合类 | 178篇 |
化学工业 | 828篇 |
金属工艺 | 135篇 |
机械仪表 | 157篇 |
建筑科学 | 263篇 |
矿业工程 | 65篇 |
能源动力 | 156篇 |
轻工业 | 241篇 |
水利工程 | 36篇 |
石油天然气 | 239篇 |
武器工业 | 36篇 |
无线电 | 423篇 |
一般工业技术 | 627篇 |
冶金工业 | 407篇 |
原子能技术 | 54篇 |
自动化技术 | 451篇 |
出版年
2024年 | 15篇 |
2023年 | 59篇 |
2022年 | 84篇 |
2021年 | 98篇 |
2020年 | 84篇 |
2019年 | 55篇 |
2018年 | 89篇 |
2017年 | 115篇 |
2016年 | 79篇 |
2015年 | 103篇 |
2014年 | 163篇 |
2013年 | 245篇 |
2012年 | 197篇 |
2011年 | 243篇 |
2010年 | 195篇 |
2009年 | 213篇 |
2008年 | 207篇 |
2007年 | 210篇 |
2006年 | 207篇 |
2005年 | 193篇 |
2004年 | 133篇 |
2003年 | 115篇 |
2002年 | 115篇 |
2001年 | 110篇 |
2000年 | 120篇 |
1999年 | 131篇 |
1998年 | 154篇 |
1997年 | 114篇 |
1996年 | 123篇 |
1995年 | 86篇 |
1994年 | 88篇 |
1993年 | 72篇 |
1992年 | 51篇 |
1991年 | 30篇 |
1990年 | 31篇 |
1989年 | 28篇 |
1988年 | 17篇 |
1987年 | 26篇 |
1986年 | 16篇 |
1985年 | 11篇 |
1984年 | 6篇 |
1983年 | 3篇 |
1982年 | 9篇 |
1981年 | 8篇 |
1980年 | 11篇 |
1979年 | 2篇 |
1977年 | 3篇 |
1976年 | 2篇 |
1975年 | 4篇 |
1970年 | 4篇 |
排序方式: 共有4479条查询结果,搜索用时 15 毫秒
1.
Cho-Yi Chen Masaoki Kawasumi Tien-Yun Lan Chi-Lam Poon Yi-Sian Lin Pin-Jou Wu Yao-Chung Chen Bing-Hong Chen Cheng-Hsien Wu Jeng-Fan Lo Rueyhung Roc Weng Yi-Chen Sun Kai-Feng Hung 《International journal of molecular sciences》2021,22(1)
Endoplasmic reticulum (ER) stress response is an adaptive program to cope with cellular stress that disturbs the function and homeostasis of ER, which commonly occurs during cancer progression to late stage. Late-stage cancers, mostly requiring chemotherapy, often develop treatment resistance. Chemoresistance has been linked to ER stress response; however, most of the evidence has come from studies that correlate the expression of stress markers with poor prognosis or demonstrate proapoptosis by the knockdown of stress-responsive genes. Since ER stress in cancers usually persists and is essentially not induced by genetic manipulations, we used low doses of ER stress inducers at levels that allowed cell adaptation to occur in order to investigate the effect of stress response on chemoresistance. We found that prolonged tolerable ER stress promotes mesenchymal–epithelial transition, slows cell-cycle progression, and delays the S-phase exit. Consequently, cisplatin-induced apoptosis was significantly decreased in stress-adapted cells, implying their acquisition of cisplatin resistance. Molecularly, we found that proliferating cell nuclear antigen (PCNA) ubiquitination and the expression of polymerase η, the main polymerase responsible for translesion synthesis across cisplatin-DNA damage, were up-regulated in ER stress-adaptive cells, and their enhanced cisplatin resistance was abrogated by the knockout of polymerase η. We also found that a fraction of p53 in stress-adapted cells was translocated to the nucleus, and that these cells exhibited a significant decline in the level of cisplatin-DNA damage. Consistently, we showed that the nuclear p53 coincided with strong positivity of glucose-related protein 78 (GRP78) on immunostaining of clinical biopsies, and the cisplatin-based chemotherapy was less effective for patients with high levels of ER stress. Taken together, this study uncovers that adaptation to ER stress enhances DNA repair and damage tolerance, with which stressed cells gain resistance to chemotherapeutics. 相似文献
2.
The design of a microstrip‐fed annular‐ring slot antenna (ARSA) with circular polarization (CP) radiation is initially studied. To obtain CP radiation with broad 3‐dB axial ratio (AR) bandwidth that can cover the WiMAX 2.3 GHz (2305–2320 MHz, 2345–2360 MHz) and WLAN 2.4 GHz (2400–2480 MHz) bands, a novel technique of extending an inverted L‐shaped slot from the bottom section of the annular‐ring is proposed. To suppress the harmonic modes induced by the CP ARSA, the technique of integrating a defected ground structure into the annular‐ring slot is further introduced. From the measured results, 10‐dB impedance bandwidth and 3‐dB AR bandwidth of 44.86 and 9.68% were achieved by the proposed harmonic suppressed CP ARSA. Furthermore, average gain and radiation efficiency of ~4.7 dBic and 71%, respectively, were also exhibited across the bands of interest. © 2014 Wiley Periodicals, Inc. Int J RF and Microwave CAE 25:337–345, 2015. 相似文献
3.
4.
中原油田岩石可钻性与声波时差关系研究 总被引:3,自引:0,他引:3
选取中原油田的大量岩心,采用常规岩石力学测试方法测定了岩石的可钻性、声波测试方法测定了岩石和岩屑声波时差,通过对测得的岩石可钻性级值和声波时差进行回归拟合,得出了中原油田岩石可钻性与声波时差的关系式。现场应用表明,该关系式较好地反映了中原油田地层岩石可钻性与声波时差的关系,可以在优选钻头时作为参考或直接应用。 相似文献
5.
Jui-Ting Weng Jiunn Ru Lai Wanjiun Liao 《Wireless Communications, IEEE Transactions on》2006,5(7):1676-1684
In this paper, we analyze node mobility for reliable packet delivery in mobile IP networks. In mobile IP, packets destined to roaming nodes are intercepted by their home agents and delivered via tunneling to their care of addresses (CoA). A mobile node may roam across multiple subnets. At each boundary crossing, a handoff is initiated such that the CoA is updated and a new tunnel is established. We consider both basic mobile IP handoff and smooth handoff. We find that reliable packet delivery in mobile IP networks can be modeled as a renewal process, because the retransmission over a new tunnel after each boundary crossing is independent of the previous history. We then derive the probability distribution of boundary crossings for each successful packet, based on which the packet reliable delivery time can be obtained. Our analytical model is derived based on a general distribution of residence time in a subnet and a general distribution of successful retransmission attempts in each subnet. The results can be readily applied to any distributions for both items. We also provide numerical examples to calculate the probability distribution of boundary crossings, and conduct simulations to validate our analytical results 相似文献
6.
Initial geopolymeric reaction processes governing dissolution of solid aluminosilicate particles in alkali solutions have
been investigated using conventional experimental techniques, and the data analysed by speciation predictions of the partial
charge model (PCM). For metakaolin powders activated with 5.0 M NaOH, solid-state nuclear magnetic resonance (NMR) spectra
disclose the existence of monomeric [Al(OH)4]− species after two hours of dissolution, consistent with PCM predictions. However, no equivalent monomeric silicate species
were observed for 5.0–10.0 M NaOH activator solutions characteristic of systems with nominal Si/Al ≤ 1. The apparent absence
of monomeric silicate species suggest rapid condensation of silicate units with [Al(OH)4]− to generate aluminosilicate species, as indicated by the evolution of the shoulder at around −87 ppm in the 29Si NMR spectra. Of the two possible stable silicate species [SiO2(OH)2]2− and [SiO(OH)3]−, the latter appears most likely to condense with [Al(OH)4]− to produce aluminosilicate oligomers, from which larger oligomers subsequently form through further condensation with [Al(OH)4]− leading to a gradual build up of aluminosilicate networks and a lowering of system alkalinity. This dissolution and hydrolysis
sequence at the early stages of synthesis suggests a reaction path wholly consistent with predictions of the partial charge
model. 相似文献
7.
8.
Qing-Huo Liu Anderson B. Weng Cho Chew 《Geoscience and Remote Sensing, IEEE Transactions on》1994,32(3):494-498
The authors formulate and implement a numerical mode-matching (NMM) method to model electrode-type resistivity tools in invaded thin beds. The authors derive the low-frequency approximation of the Maxwell's equations to obtain the partial differential equation for the potential field. The new NMM program is validated by comparing the numerical results with those obtained from other dc programs. It is found that this new program is much faster than the program using the finite-element method (FEM), and hence is useful for routine interpretation of resistivity logs and for inversion 相似文献
9.
10.
The mechanisms of speciation of aluminate and silicate phases during dissolution and condensation stages of alumino-silicate
geopolymer reactions characterised by Si/Al ≥ 3, have been investigated and the results compared to predictions of the partial
charge model. Solid-state nuclear magnetic resonance (NMR) traces indicate that free [Al(OH)4]− species, present in lower silicate formulations such as Si/Al ≤ 1, do not occur in the present systems, suggesting that the condensation reaction between [Al(OH)4]− and silicate species is fairly quick and is consumed as soon as it is formed. This observation is also consistent with both
calorimetric measurements and model predictions, as the condensation time increased exponentially with increased Si/Al ratio
in the geopolymeric phase, indicating again that the high content of Al species in the gel phase greatly enhanced the condensation
rate. The experimental observations suggest that the condensation process in these systems occurs in two stages: (a) quick
condensation between aluminate and silicate species; followed by (b) a slow condensation stage solely involving silicate species. 相似文献