全文获取类型
收费全文 | 4942篇 |
免费 | 208篇 |
国内免费 | 27篇 |
专业分类
电工技术 | 57篇 |
综合类 | 32篇 |
化学工业 | 741篇 |
金属工艺 | 82篇 |
机械仪表 | 179篇 |
建筑科学 | 94篇 |
矿业工程 | 5篇 |
能源动力 | 111篇 |
轻工业 | 293篇 |
水利工程 | 15篇 |
石油天然气 | 15篇 |
无线电 | 417篇 |
一般工业技术 | 554篇 |
冶金工业 | 2234篇 |
原子能技术 | 52篇 |
自动化技术 | 296篇 |
出版年
2024年 | 5篇 |
2023年 | 41篇 |
2022年 | 91篇 |
2021年 | 116篇 |
2020年 | 74篇 |
2019年 | 79篇 |
2018年 | 96篇 |
2017年 | 110篇 |
2016年 | 102篇 |
2015年 | 98篇 |
2014年 | 125篇 |
2013年 | 167篇 |
2012年 | 180篇 |
2011年 | 224篇 |
2010年 | 180篇 |
2009年 | 163篇 |
2008年 | 163篇 |
2007年 | 103篇 |
2006年 | 102篇 |
2005年 | 80篇 |
2004年 | 83篇 |
2003年 | 77篇 |
2002年 | 76篇 |
2001年 | 71篇 |
2000年 | 51篇 |
1999年 | 111篇 |
1998年 | 696篇 |
1997年 | 468篇 |
1996年 | 296篇 |
1995年 | 181篇 |
1994年 | 147篇 |
1993年 | 140篇 |
1992年 | 43篇 |
1991年 | 40篇 |
1990年 | 21篇 |
1989年 | 33篇 |
1988年 | 39篇 |
1987年 | 32篇 |
1986年 | 21篇 |
1985年 | 13篇 |
1984年 | 4篇 |
1983年 | 6篇 |
1982年 | 11篇 |
1981年 | 15篇 |
1980年 | 17篇 |
1979年 | 4篇 |
1978年 | 5篇 |
1977年 | 48篇 |
1976年 | 123篇 |
1975年 | 3篇 |
排序方式: 共有5177条查询结果,搜索用时 140 毫秒
1.
2.
Ha ABDEL MAKSOUD Mk MAHFOUZ Mi SOLIMAN Mohamed G ELHARRIF M ABBASS Ma EL-BADRY 《Biocell》2020,44(1):111-115
Pyrethroid esters are widely used as insecticides worldwide. In this study, we aimed to evaluate the harmful
effect of deltamethrin on the male reproductive system through the assessment of reproductive hormones, inflammatory
markers, and testicular function. To achieve our aim, eighty male 7-9-week-old, Wistar rats were taken, weighed, and
divided into four experimental groups. The first group was kept as a control group, and the other three groups were
given deltamethrin orally at different concentrations (0.87, 8.7, and 17.4 mg/kg body weight) for nine weeks. The results
indicated that deltamethrin administration associated with a significant decrease in reproductive hormones, especially
FSH, LH, and significant elevation in the interleukin 2 (IL2), interleukin 6 (IL6), histamine, and cortisol levels. Also, the
significance of inhibition of sperm motility and viability, decreased testis weights, sperm count, and fructose in semen
were noted. These findings clarify the harmful effect of deltamethrin on the male reproductive system by producing a
significant alteration in reproductive hormones, inflammatory markers as well as testicular function. 相似文献
3.
Effect of Supports and Promoters on the Performance of Ni-Based Catalysts in Ethanol Steam Reforming
Thanh Khoa Phung Thong Le Minh Pham Anh-Nga T. Nguyen Khanh B. Vu Ha Ngoc Giang Tuan-Anh Nguyen Thanh Cong Huynh Hong Duc Pham 《化学工程与技术》2020,43(4):672-688
Ethanol steam reforming (ESR) is one of the potential processes to convert ethanol into valuable products. Hydrogen produced from ESR is considered as green energy for the future and can be an excellent alternative to fossil fuels with the aim of mitigating the greenhouse gas effect. The ESR process has been well studied, using transition metals as catalysts coupled with both acidic and basic oxides as supports. Among various reported transition metals, Ni is an inexpensive material with activity comparable to that of noble metals, showing promising ethanol conversion and hydrogen yields. Additionally, different promoters and supports were utilized to enhance the hydrogen yield and the catalyst stability. This review summarizes and discusses the influences of the supports and promoters of Ni-based catalysts on the ESR process. 相似文献
4.
Jeong-Soo Lee Yang-Kyu Choi Daewon Ha Balasubramanian S. Tsu-Jae King Bokor J. 《Electron Device Letters, IEEE》2003,24(3):186-188
The hydrogen annealing process has been used to improve surface roughness of the Si-fin in CMOS FinFETs for the first time. Hydrogen annealing was performed after Si-fin etch and before gate oxidation. As a result, increased saturation current with a lowered threshold voltage and a decreased low-frequency noise level over the entire range of drain current have been attained. The low-frequency noise characteristics indicate that the oxide trap density is reduced by a factor of 3 due to annealing. These results suggest that hydrogen annealing is very effective for improving device performance and for attaining a high-quality surface of the etched Si-fin. 相似文献
5.
Z Abbas AH Khan SM Jafri SS Hamid SH Shah S Abid JA Qureshi 《Canadian Metallurgical Quarterly》1997,12(11):703-706
The authors compared in a controlled clinical study two groups of patients after a first renal transplantation treated by triple drug immunosuppressive therapy. In a group of 31 patients the triple combination comprised Sandimmune Neoral. In the control group there were 30 patients who received Sandimmune. No differences were found between the two groups as regards the effectiveness of this treatment and the authors did not confirm a lower incidence of rejections described in patients treated with Sandimmune Neoral. They confirmed, however, a lower interindividual variability of Cy-A levels assessed specifically in patients treated with Sandimmune Neoral. 相似文献
6.
LJ Huang K Durick JA Weiner J Chun SS Taylor 《Canadian Metallurgical Quarterly》1997,94(21):11184-11189
Subcellular localization directed by specific A kinase anchoring proteins (AKAPs) is a mechanism for compartmentalization of cAMP-dependent protein kinase (PKA). Using a two-hybrid screen, a novel AKAP was isolated. Because it interacts with both the type I and type II regulatory subunits, it was defined as a dual specific AKAP or D-AKAP1. Here we report the cloning and characterization of another novel cDNA isolated from that screen. This new member of the D-AKAP family, D-AKAP2, also binds both types of regulatory subunits. A message of 5 kb pairs was detected for D-AKAP2 in all embryonic stages and in all adult tissues tested. In brain, skeletal muscle, kidney, and testis, a 10-kb mRNA was identified. In testis, several small mRNAs were observed. Therefore, D-AKAP2 represents a novel family of proteins. cDNA cloning from a mouse testis library identified the full length D-AKAP2. It is composed of 372 amino acids which includes the R binding fragment, residues 333-372, at its C-terminus. Based on coprecipitation assays, the R binding domain interacts with the N-terminal dimerization domain of RIalpha and RIIalpha. A putative RGS domain was identified near the N-terminal region of D-AKAP2. The presence of this domain raises the intriguing possibility that D-AKAP2 may interact with a Galpha protein thus providing a link between the signaling machinery at the plasma membrane and the downstream kinase. 相似文献
7.
8.
Semi‐Markovian processes (SMP) serve as a versatile means to model various traffic types generated by sources or superposed
from links in ATM networks. An efficient discrete time analysis method is proposed for SMP/G/1 queueing systems to evaluate
ATM switches with non‐renewal input. Some basic results are derived for the autocorrelation function of semi‐Markovian processes
and for the effect of state space reduction on autocorrelation, which show how to represent correlated traffic with given
characteristic by an adequate SMP model of limited size.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
9.
RB Singh R Beegom S Ghosh MA Niaz V Rastogi SS Rastogi NK Singh S Nangia 《Canadian Metallurgical Quarterly》1997,11(10):679-685
OBJECTIVES: To determine age-specific prevalence of hypertension and blood pressure (BP) levels in relation to diet and lifestyle factors in North Indians. DESIGN AND SETTING: Cross-sectional survey in 20 randomly selected streets in Moradabad, North India. SUBJECTS AND METHODS: A total of 1806 subjects from North India (904 males and 902 females) age range 25-64 years. The survey methods were as follows: dietary diaries for 7 days food intake record; BP measurements; physician administered questionnaire and anthropometric measurements. Diagnosis of hypertension was based on new World Health Organization/International Society of Hypertension (WHO/ISH) criteria. Risk factors were assessed based on WHO guidelines. RESULTS: The prevalence of hypertension according to WHO/ISH criteria was 23.7% and by old WHO criteria 13.3%. In the WHO/ISH hypertensive group, isolated diastolic hypertension was present in 47.3% males and 40.6% females. Males have a slightly higher prevalence than females in the young age group, however, the prevalence rates are comparable in the older age groups. In both sexes, the prevalence rates and BP level increased with older age. Multivariate analysis revealed that age, higher body mass index, central obesity and higher socioeconomic status were independently and strongly associated with hypertension in both sexes. Higher dietary fat and salt intake and lower physical activity were weakly but significantly associated with hypertension. CONCLUSION: Association of higher socioeconmic status, higher body mass index and central obesity in North Indian adults with higher fat intake, lower physical activity and higher prevalence and level of hypertension indicate that these populations may benefit by decreasing the dietary fat intake and increasing physical activity, with an aim to decrease central obesity for decreasing hypertension in North Indians. 相似文献
10.
Anna Hać 《Journal of Network and Systems Management》1994,2(1):49-62
This paper analyzes the performance of a switching architecture. The performance measures include the elapsed time of packet transfer and the waiting time to begin transfer. The architecture is partitioned depending on the type of network used and the expected traffic in the network. Every partition has a switch with a buffer that can absorb surges of bursty traffic within the network partition. The buffer size depends on the type of the network and incoming traffic. The partition size depends on the network bandwidth, network traffic, packet size and buffer size. Examples of different networks are used to show the applications of the model. The results show that the elapsed time of packet switch transfer depends exponentially on the number of partitions in the network. 相似文献