首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   2412篇
  免费   45篇
  国内免费   5篇
电工技术   12篇
综合类   3篇
化学工业   106篇
金属工艺   26篇
机械仪表   35篇
建筑科学   11篇
矿业工程   1篇
能源动力   13篇
轻工业   84篇
水利工程   19篇
石油天然气   7篇
无线电   81篇
一般工业技术   83篇
冶金工业   1916篇
原子能技术   9篇
自动化技术   56篇
  2023年   3篇
  2022年   8篇
  2021年   17篇
  2020年   11篇
  2019年   17篇
  2018年   15篇
  2017年   15篇
  2016年   20篇
  2015年   23篇
  2014年   30篇
  2013年   39篇
  2012年   40篇
  2011年   44篇
  2010年   34篇
  2009年   37篇
  2008年   27篇
  2007年   21篇
  2006年   17篇
  2005年   12篇
  2004年   23篇
  2003年   22篇
  2002年   13篇
  2001年   11篇
  2000年   11篇
  1999年   61篇
  1998年   670篇
  1997年   302篇
  1996年   227篇
  1995年   119篇
  1994年   99篇
  1993年   123篇
  1992年   11篇
  1991年   24篇
  1990年   31篇
  1989年   32篇
  1988年   33篇
  1987年   27篇
  1986年   15篇
  1985年   14篇
  1984年   1篇
  1983年   3篇
  1982年   4篇
  1981年   12篇
  1980年   13篇
  1979年   1篇
  1978年   1篇
  1977年   24篇
  1976年   103篇
  1956年   1篇
  1955年   1篇
排序方式: 共有2462条查询结果,搜索用时 31 毫秒
991.
The ultrastructure of autonomic nerve fibers and terminal varicosities is described in relation to the lamina propria of the human seminiferous tubules during childhood (age 3 to 10 years). Autonomic nerve varicosities are classified as: Type I with numerous small (30-60 nm) agranular vesicles and variable numbers of large (100 nm) granular vesicles, and Type II with numerous small (30-60 nm) granular vesicles and sporadic large granular vesicles. These two varicosity types are consistent in morphology with cholinergic and adrenergic nerve terminals, respectively. Nerve varicosities are found, associated with Schwann cells, in proximity to the cells of the lamina propria. Although not found in direct "synaptic' contact, these autonomic endings are often within a few hundred nanometers of the cellularity of the lamina propria. The Schwannian sheath is interrupted over the varicosities at these sites and occasionally the terminal varicosities are totally lacking a Schwann sheath. These findings are consistent with the structural relationship of autonomic nerve "terminals' and effector in other endocrine and non-endocrine systems. This is the first evidence of adrenergic nerve varicosities in proximity to the lamina propria in humans (at any age). Evidence is also presented which suggests a locational difference in the distribution of cholinergic (Type I) and adrenergic (Type II) nerve varicosities in this region, with only cholinergic endings observed directly adjacent to the basal lamina of the seminiferous tubules.  相似文献   
992.
Unicompartmental knee arthroplasty is an appropriate method of treating selected patients with osteoarthritis of the medial compartment of the knee. The common causes of failure are aseptic loosening, infection, patellofemoral pain, and deterioration in the opposite compartment. Seven cases of a cohort of 32 Robert Brigham unicondylar knee replacements that failed because of early catastrophic wear of the polyethylene tibial component are reported. Possible reasons suggested for failure include inadequate thickness of polyethylene, fusion defects in the polyethylene structure as a result of the sterilization process, increased rotational freedom, and reduced conformity in the design of the prosthesis.  相似文献   
993.
2'-Azido-2'-deoxyuridine and 2'-azido-2'-deoxycytidine were evaluated for their inhibitory activity against ribonucleotide reductase and for subsequent cell growth inhibition. Their mono- and di-phosphates were synthesized and their inhibitory activities against the reductase were also determined in a permeabilized cell system, along with the two nucleosides. The results of the present study identify the first phosphorylation step involved in the conversion of the two azidonucleosides to the corresponding diphosphates to be rate-limiting in the overall activation.  相似文献   
994.
利用X射线双能量进行物质属性的判别,是机场、车站行李安全检查的一项基本技术.未经滤波的单个140KV的X射线源,发射的是连续能谱的X射线,采用两种不同能谱响应的探测器分别得到高低能量的透射信号.综合考虑连续能谱效应和探测器效率的影响,推导出高低能量的线性衰减系数比值的逼近多项式,对于固定的射线源和探测器这个多项式的各个系数是不变的.利用这种方法对物质属性进行判别,并给出了实验结果.  相似文献   
995.
The volatile composition and properties of wine made using the ‘Cheongsoo’ grape cultivar harvested at different stages of ripening were evaluated. There were changes in the chemical composition of ‘Cheongsoo’ wine, including pH, total acidity, total polyphenols, and tannins according to the degree of grape ripening. Colorimetric analysis indicated that wines had yellow tones and deep and very strong colors with a high chromatic intensity depending on the degree of grape ripening. Of 87 detected flavor compounds, 26 had high OAV (odor active values). Based on OAV, 26 compounds were considered to be important odorants for ‘Cheongsoo’ wine. A harvest date of September 19 showed good separation from August 29 and September 8 and 29, depending on the degree of grape ripening, on a principle components analysis plot for grape ripening. More volatile compounds were present in September 19 harvested grapes.  相似文献   
996.
One of the important considerations for the development of on‐chip batteries is the need to photopattern the solid electrolyte directly on electrodes. Herein, the photopatterning of a lithium‐ion conducting solid electrolyte is demonstrated by modifying a well‐known negative photoresist, SU‐8, with LiClO4. The resulting material exhibits a room temperature ionic conductivity of 52 µS cm?1 with a wide electrochemical window (>5 V). Half‐cell galvanostatic testing of 3 µm thin films spin‐coated on amorphous silicon validates its use for on‐chip energy‐storage applications. The modified SU‐8 possesses excellent mechanical integrity, is thermally stable up to 250 °C, and can be photopatterned with micrometer‐scale resolution. These results present a promising direction for the integration of electrochemical energy storage in microelectronics.  相似文献   
997.
Although allogenic meniscus grafting can be immunologically safe, it causes immune rejection due to an imbalanced tissue supply between donor and recipient. Pigs are anatomically and physiologically similar to adult humans and are, therefore, considered to be advantageous xenotransplantation models. However, immune rejection caused by genetic difference damages the donor tissue and can sometimes cause sudden death. Immune rejection is caused by genes; porcine GGTA1, CMAH, and B4GLANT2 are the most common. In this study, we evaluated immune cells infiltrating the pig meniscus transplanted subcutaneously into BALB/c mice bred for three weeks. We compared the biocompatibility of normal Jeju native black pig (JNP) meniscus with that of triple knockout (TKO) JNP meniscus (α-gal epitope, N-glycolylneuraminic acid (Neu5Gc), and Sd (a) epitope knockout using CRISPR-Cas 9). Mast cells, eosinophils, neutrophils, and macrophages were found to have infiltrated the transplant boundary in the sham (without transplantation), normal (normal JNP), and test (TKO JNP) samples after immunohistochemical analysis. When compared to normal and sham groups, TKO was lower. Cytokine levels did not differ significantly between normal and test groups. Because chronic rejection can occur after meniscus transplantation associated with immune cell infiltration, we propose studies with multiple genetic editing to prevent immune rejection.  相似文献   
998.
For patients who suffer from sensorineural hearing loss by damaged or loss of hair cells in the cochlea, biomimetic artificial cochleas to remedy the dis­advantages of existing implant systems have been intensively studied. Here, a new concept of an inorganic‐based piezoelectric acoustic nanosensor (iPANS) for the purpose of a biomimetic artificial hair cell to mimic the functions of the original human hair cells is introduced. A trapezoidal silicone‐based membrane (SM) mimics the function of the natural basilar membrane for frequency selectivity, and a flexible iPANS is fabricated on the SM utilizing a laser lift‐off technology to overcome the brittle characteristics of inorganic piezoelectric materials. The vibration amplitude vs piezoelectric sensing signals are theoretically examined based on the experimental conditions by finite element analysis. The SM is successful at separating the audible frequency range of incoming sound, vibrating distinctively according to varying locations of different sound frequencies, thus allowing iPANS to convert tiny vibration displacement of ≈15 nm into an electrical sensing output of ≈55 μV, which is close to the simulation results presented. This conceptual iPANS of flexible inorganic piezoelectric materials sheds light on the new fields of nature‐inspired biomimetic systems using inherently high piezoelectric charge constants.  相似文献   
999.
The objective of this study was to investigate the influence of yeast strains on the physicochemical characteristics, methanol and acetaldehyde profiles, and volatile compounds of Korean rice distilled spirits. Ten yeast strains were employed for the brewing of distilled spirits and the resulting products were filtered and distilled twice. The amounts of methanol and acetaldehyde for the ten yeasts showed different profiles. Higher amounts of methanol were detected for strains CL, CY, DV, BD, ED and LP, while EC, D2, D4 and RH had <2 mg L?1 methanol content. Strains D2, BD and ED produced the lowest amounts of acetaldehyde. The head portions of the spirits, which started in the fraction that contained <5 mg L?1 of acetaldehyde, were between 7.7% (BD) and 18.2% (LP) of the total fractions. Strains D2, CL and CY produced more alcohol in the body fraction than the other yeasts. The major volatile compounds were esters in the form of fatty acid ethyl esters, such as ethyl palmitate, ethyl myristate and ethyl oleate. Isoamyl alcohol, which is an important volatile compound for rice wine, occupied 0.91–2.24% of the relative peak areas. Strain D2, of the strains tested, appeared to be the most appropriate yeast for Korean distilled spirit based on alcohol production and the high relative peak area of volatile compounds, except for ethanol. Strains CL and CY could also be considered for producing high‐quality Korean rice distilled spirits with efficiency and flavour. Copyright © 2015 The Institute of Brewing & Distilling  相似文献   
1000.
Marfan syndrome (MFS) is an autosomal dominant disease that affects the skeletal, ocular and cardiovascular systems. Defects in the gene that codes for fibrillin (FBN-1) are responsible for MFS. Here we report the world's first use of preimplantation genetic testing (PGT) to achieve a clinical pregnancy and live birth of a baby free of a Marfan mutation. One or two blastomeres from each embryo were tested for a CA repeat within the FBN-1 gene. The prospective mother is homozygous for the CA repeat (2/2) and has two normal copies of the FBN-1 gene, while the prospective father is heterozygous for the CA repeat (1/2), and is affected with the Marfan syndrome. In the father's family, allele 2 segregates with the mutated FBN-1 gene. For PGT, any embryo diagnosed as heterozygous for the CA repeat (1/2) would be presumed to have inherited normal FBN-1 genes from the father and the mother and be unaffected. One in-vitro fertilization (IVF) cycle yielded 12 embryos for preimplantation testing; six of the embryos were heterozygous for the CA repeat (1/2) and presumed to be free of the Marfan mutation. Five of the six embryos were subsequently transferred into the uterus. The fetus was tested by chorionic villus sampling and found to be free of the Marfan mutation by the same linkage analysis, had a normal fetal echocardiogram, and was normal at birth.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号