全文获取类型
收费全文 | 3690篇 |
免费 | 46篇 |
国内免费 | 1篇 |
专业分类
电工技术 | 29篇 |
综合类 | 1篇 |
化学工业 | 260篇 |
金属工艺 | 40篇 |
机械仪表 | 27篇 |
建筑科学 | 68篇 |
矿业工程 | 9篇 |
能源动力 | 67篇 |
轻工业 | 184篇 |
水利工程 | 16篇 |
石油天然气 | 14篇 |
无线电 | 220篇 |
一般工业技术 | 277篇 |
冶金工业 | 2276篇 |
原子能技术 | 34篇 |
自动化技术 | 215篇 |
出版年
2022年 | 13篇 |
2020年 | 17篇 |
2019年 | 14篇 |
2018年 | 26篇 |
2017年 | 18篇 |
2016年 | 14篇 |
2015年 | 22篇 |
2014年 | 32篇 |
2013年 | 74篇 |
2012年 | 49篇 |
2011年 | 73篇 |
2010年 | 54篇 |
2009年 | 65篇 |
2008年 | 69篇 |
2007年 | 60篇 |
2006年 | 55篇 |
2005年 | 55篇 |
2004年 | 29篇 |
2003年 | 45篇 |
2002年 | 40篇 |
2001年 | 44篇 |
2000年 | 43篇 |
1999年 | 75篇 |
1998年 | 643篇 |
1997年 | 413篇 |
1996年 | 267篇 |
1995年 | 167篇 |
1994年 | 165篇 |
1993年 | 145篇 |
1992年 | 42篇 |
1991年 | 49篇 |
1990年 | 45篇 |
1989年 | 47篇 |
1988年 | 41篇 |
1987年 | 49篇 |
1986年 | 35篇 |
1985年 | 46篇 |
1984年 | 17篇 |
1983年 | 28篇 |
1982年 | 22篇 |
1981年 | 44篇 |
1980年 | 34篇 |
1979年 | 30篇 |
1978年 | 26篇 |
1977年 | 75篇 |
1976年 | 163篇 |
1975年 | 29篇 |
1974年 | 15篇 |
1973年 | 17篇 |
1971年 | 13篇 |
排序方式: 共有3737条查询结果,搜索用时 0 毫秒
991.
J. D. H. Keatinge R.-Y. Yang J. d’A. Hughes W. J. Easdown R. Holmer 《Food Security》2011,3(4):491-501
A nutritious and varied diet is a critical means by which good health can be maintained. Consumption of less than 200 g of
vegetables per person per day in many countries today is common and this low amount, often in conjunction with poverty and
poor medical services, is associated with unacceptable levels of mortality and malnutrition in preschool children and other
vulnerable groups. An increase in the availability, affordability and consumption of nutrient-dense vegetables and pulses
is one way malnutrition may be substantially reversed—yet nutritional security appears to be less valued than food security
by key decision makers, and vegetable crops thus receive inadequate research investment. Opportunities exist for the poor
to improve their access to vegetables, particularly if they are willing to grow home gardens. Research continues on defining
appropriate nutrient-dense vegetables for such activities, but these efforts may be compromised by failure to adopt good agricultural
practices, resulting in contamination and unhealthy produce for producers and consumers. The scientific community is ready
to play its role in battling malnutrition and hunger, but unless the political resolve can be found to support the causes
of both food and nutritional security together, it is unlikely that the Millennium Development Goals will be achieved in a
timely fashion. Redressing the current imbalance in agricultural investment can improve efficiency in food production and
ensure nutritious diets can be a reality for all people. 相似文献
992.
Lammert R.M. Jones A.M. Youtsey C.T. Hughes J.S. Roh S.D. Adesida I. Coleman J.J. 《Photonics Technology Letters, IEEE》1997,9(11):1445-1447
The design and operation of InGaAsP-InP ridge-waveguide (RW) distributed Bragg reflector (DBR) multiple quantum-well lasers with first-order surface gratings are presented. The RW DBR lasers are fabricated using only a single growth step without growth on a corrugated surface. Uncoated devices with grating etch depths of 0.6 and 0.5-μm exhibit pulsed threshold currents of 32 and 43 mA with slope efficiencies of 0.34 and 0.24 W/A, respectively. The device with a grating etch depth of 0.5-μm operates on a single longitudinal mode with about 40 dB side-mode suppression. All these results are from devices with Bragg condition wavelengths which are red-shifted from the peak spontaneous emission wavelength by over 400 Å 相似文献
993.
Florine Seidel Robert Kleemann Wim van Duyvenvoorde Nikki van Trigt Nanda Keijzer Sandra van der Kooij Cees van Kooten Lars Verschuren Aswin Menke Amanda J. Kiliaan Johnathan Winter Timothy R. Hughes B. Paul Morgan Frank Baas Kees Fluiter Martine C. Morrison 《International journal of molecular sciences》2022,23(18)
Background: Chronic inflammation is an important driver in the progression of non-alcoholic steatohepatitis (NASH) and atherosclerosis. The complement system, one of the first lines of defense in innate immunity, has been implicated in both diseases. However, the potential therapeutic value of complement inhibition in the ongoing disease remains unclear. Methods: After 20 weeks of high-fat diet (HFD) feeding, obese Ldlr-/-.Leiden mice were treated twice a week with an established anti-C5 antibody (BB5.1) or vehicle control. A separate group of mice was kept on a chow diet as a healthy reference. After 12 weeks of treatment, NASH was analyzed histopathologically, and genome-wide hepatic gene expression was analyzed by next-generation sequencing and pathway analysis. Atherosclerotic lesion area and severity were quantified histopathologically in the aortic roots. Results: Anti-C5 treatment considerably reduced complement system activity in plasma and MAC deposition in the liver but did not affect NASH. Anti-C5 did, however, reduce the development of atherosclerosis, limiting the total lesion size and severity independently of an effect on plasma cholesterol but with reductions in oxidized LDL (oxLDL) and macrophage migration inhibitory factor (MIF). Conclusion: We show, for the first time, that treatment with an anti-C5 antibody in advanced stages of NASH is not sufficient to reduce the disease, while therapeutic intervention against established atherosclerosis is beneficial to limit further progression. 相似文献
994.
Vincent Kuek Anastasia M. Hughes Rishi S. Kotecha Laurence C. Cheung 《International journal of molecular sciences》2021,22(13)
In recent decades, the conduct of uniform prospective clinical trials has led to improved remission rates and survival for patients with acute myeloid leukaemia and acute lymphoblastic leukaemia. However, high-risk patients continue to have inferior outcomes, where chemoresistance and relapse are common due to the survival mechanisms utilised by leukaemic cells. One such mechanism is through hijacking of the bone marrow microenvironment, where healthy haematopoietic machinery is transformed or remodelled into a hiding ground or “sanctuary” where leukaemic cells can escape chemotherapy-induced cytotoxicity. The bone marrow microenvironment, which consists of endosteal and vascular niches, can support leukaemogenesis through intercellular “crosstalk” with niche cells, including mesenchymal stem cells, endothelial cells, osteoblasts, and osteoclasts. Here, we summarise the regulatory mechanisms associated with leukaemia–bone marrow niche interaction and provide a comprehensive review of the key therapeutics that target CXCL12/CXCR4, Notch, Wnt/b-catenin, and hypoxia-related signalling pathways within the leukaemic niches and agents involved in remodelling of niche bone and vasculature. From a therapeutic perspective, targeting these cellular interactions is an exciting novel strategy for enhancing treatment efficacy, and further clinical application has significant potential to improve the outcome of patients with leukaemia. 相似文献
995.
J. Zhang W. Jack Hughes A. C. Hladky-Hennion Robert E. Newnham 《Materials Research Innovations》1999,2(5):252-255
A new type of cymbal transducer, called the concave cymbal, has been developed to increase the pressure tolerance and reliability
of the transducer under high hydrostatic pressure. The main feature of the new design is a lead zirconate titanate ceramic
ring sandwiched between two concave metal endcaps. It shows much improved pressure performance and can withstand a pressure
of up to 6 MPa while maintaining high effective hydrostatic piezoelectric coefficients. When incorporated into a planar array
with a radiating area of 5.5 cm×5.5 cm and weight of only 30 g, a transmitting voltage response of around 125 dB re 1 μPa/V
@ 1 m was obtained over a frequency range between 20 and 50 kHz.
Received: 14 October 1998 / Reviewed and accepted: 15 October 1998 相似文献
996.
Three preparative-scale gel permeation chromatography columns were constructed and filled with Corning porous-glass packing materials. Each column was packed with a different pore-size materials, CPG 10–2000, CPG 10–350, CPG 10–120, all of which had been treated with hexamethyldisilazane. An additional preparative-scale column packed with Styragel, nominal porosity 5 × 104 Å, was added to complete the column bank. Polystyrene standards were used to investigate the effects of molecular weight and sample concentration upon elution volume. A commerical polystyrene sample was fractionated using this system to study the effects of sample concentration and flow rate on fractionation efficiency. These fractions were analyzed by high-resolution analyticalscale gel permeation chromatography. Where possible, the results have been compared with similar studies that used Porasil (Spherosil) and Styragel columns. 相似文献
997.
Weights of testes and epididymides, body weight, and morphometric measurements of testicular tissue of 75 boars of a line selected for eight generations for predicted weight of testes at 150 d of age and 75 boars of a randomly selected control line were used to evaluate the effects of selection on testicular development at 70, 100, 130, 160, and 450 d of age (n = 15 boars per line per age). Body weights for boars of the select and control line did not differ (P < .05) and the shape of the body growth curve was similar for both lines. Boars of the select line had larger testes than control boars at each age (P < .05), but there was a significant line x age interaction. The percentage increase of the select line mean over the control mean for weight of testes was 37% at 70 d, a maximum of 120% at 100 d, and 25% at 450 d. The percentage of the testes made up of seminiferous tubules differed between lines (P < .01). Lines had similar means of approximately 28% at 70 d and 71% at 450 d, but the mean for the select line was larger between 100 and 160 d of age; the greatest difference was 11.6% (control = 43.7, select = 55.3%) at 100 d. After 70 d of age, select-line boars had a greater percentage of seminiferous tubules with lumens that contained elongated spermatids (P < .10).(ABSTRACT TRUNCATED AT 250 WORDS) 相似文献
998.
R. Hoover T. Hughes H.J. Chung Q. Liu 《Food research international (Ottawa, Ont.)》2010,43(2):399-413
The major carbohydrate of pulse seeds is starch, which accounts for 22–45% of the dry matter. In recent years, substantial progress has been made on the molecular structure of cereal and tuber starches and their impact on functionality. Similar studies on pulse starches are limited. This review summarizes the present status of knowledge on the isolation, composition, molecular structure, properties and modification of pulse starches. Future research needs in the area of pulse starches are outlined. 相似文献
999.
S. Dhawan V. W. Hughes D. Kawall W. Liu J. Pretz R. Sumner 《Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment》2000,450(2-3):391-398
We have developed and tested a 4 channel, 500 MHz, 512 k sample, 8 bit waveform digitizer in a FASTCAMAC module. A novel feature is the implementation of a sparse scan during readout with a programmable differential trigger to reduce the data to a manageable level. The differential trigger allows reliable detection of pulses with low threshold in the presence of a variable baseline. 相似文献
1000.
研究了锻造态和热处理态不同成分铝基轴承合金在油润滑条件下的摩擦行为,以及材料的硬度、热处理制度和锻造对材料耐磨性的影响。所用材料是 Al-8.5Si-3.5Cu 和 Al-15Pb-3.7Cu-1.5Si-1.1Fe。在锻造过程中,应变范围为10%~20%。并对材料进行T6热处理。在销-盘式磨损试验机上对材料的摩擦性能进行测试。结果表明,锻造过程使材料的硬度得到增加;铸造应变在10%~20%的范围内对材料的摩擦磨损影响不明显。 相似文献