全文获取类型
收费全文 | 2546篇 |
免费 | 4篇 |
专业分类
电工技术 | 9篇 |
化学工业 | 33篇 |
金属工艺 | 3篇 |
机械仪表 | 2篇 |
建筑科学 | 9篇 |
矿业工程 | 1篇 |
能源动力 | 5篇 |
轻工业 | 26篇 |
水利工程 | 10篇 |
无线电 | 45篇 |
一般工业技术 | 36篇 |
冶金工业 | 2272篇 |
原子能技术 | 1篇 |
自动化技术 | 98篇 |
出版年
2021年 | 3篇 |
2020年 | 3篇 |
2019年 | 3篇 |
2018年 | 5篇 |
2017年 | 3篇 |
2016年 | 7篇 |
2014年 | 4篇 |
2013年 | 18篇 |
2012年 | 7篇 |
2011年 | 9篇 |
2010年 | 11篇 |
2009年 | 7篇 |
2008年 | 14篇 |
2007年 | 9篇 |
2006年 | 8篇 |
2005年 | 8篇 |
2004年 | 7篇 |
2003年 | 6篇 |
2002年 | 9篇 |
2001年 | 8篇 |
1999年 | 81篇 |
1998年 | 737篇 |
1997年 | 454篇 |
1996年 | 260篇 |
1995年 | 140篇 |
1994年 | 111篇 |
1993年 | 134篇 |
1992年 | 21篇 |
1991年 | 21篇 |
1990年 | 20篇 |
1989年 | 26篇 |
1988年 | 35篇 |
1987年 | 19篇 |
1986年 | 17篇 |
1985年 | 13篇 |
1983年 | 3篇 |
1982年 | 11篇 |
1981年 | 11篇 |
1980年 | 18篇 |
1978年 | 5篇 |
1977年 | 64篇 |
1976年 | 149篇 |
1975年 | 10篇 |
1974年 | 7篇 |
1972年 | 3篇 |
1971年 | 4篇 |
1968年 | 4篇 |
1967年 | 3篇 |
1965年 | 2篇 |
1955年 | 3篇 |
排序方式: 共有2550条查询结果,搜索用时 15 毫秒
981.
EM Sloand NS Young P Kumar FF Weichold T Sato JP Maciejewski 《Canadian Metallurgical Quarterly》1997,89(4):1357-1363
Direct killing of CD4+ lymphocytes by human immunodeficiency virus-1 (HIV-1) probably cannot account for the magnitude of the loss of these cells during the course of HIV-1 infection. Experimental evidence supports a pathophysiologic role of the apoptotic process in depletion of CD4 cells in acquired immunodeficiency syndrome (AIDS). The Fas-receptor/Fas-ligand (Fas-R/Fas-L) system mediates signals for apoptosis of susceptible lymphocytes and lympoblastoid cell lines. A number of investigators have recently reported increased expression of the Fas receptor in individuals with HIV infection, along with increased sensitivity of their lymphocytes to anti-Fas antibody mimicking Fas ligand. We attempted to determine the role of Fas-mediated apoptosis in disease progression and viral replication. Increased Fas-receptor (CD95) expression on CD4+ and CD8+ lymphocytes was found in a large group of HIV-1-infected patients compared with normal controls; individuals with a diagnosis of AIDS and a history of opportunistic infection had significantly more Fas receptor expression than did asymptomatic HIV-infected persons and normal blood donor controls (P < .01). Triggering of the Fas-R by agonistic anti-Fas monoclonal antibody, CH11, was preferentially associated with apoptosis in the CD4+ cells; this effect was more pronounced in lymphocytes derived from HIV+ individuals. Soluble and membrane-bound forms of Fas-L were produced in greater amounts in peripheral blood mononuclear cells (PBMC) cultures and in plasma obtained from HIV-1-infected persons than from normal controls. Furthermore, triggering of lymphocytes from HIV-infected persons by CH11 increased levels of interleukin-1beta converting enzyme (ICE), a protein associated with apoptosis. When PBMC were cultured in the presence of CH11, p24 production per number of viable cells was decreased as compared with the same PBMC without CH11 (P < .01). These findings suggest that multiple mechanisms, including increased production of Fas-L by infected PBMC, increased Fas-R expression, and induction of a protease of ICE family, may play roles in the apoptotic depletion of CD4+ cells in HIV infection. 相似文献
982.
EM Sokal T Caragiozoglou M Lamy R Reding JB Otte 《Canadian Metallurgical Quarterly》1993,56(6):1394-1398
Epstein-Barr virus serology was performed before and after transplantation in 116 patients of a total series of 261 pediatric OLT recipients. Thirty-nine percent had no immunity before OLT, but this percentage decreased to 11.2% at 6 months and 10.5% at 2 years after transplantation. In this series, 10 children developed a B cell lymphoproliferative disease. Four had adenotonsillar involvement, 2 of them with associated digestive tract invasion. Three of these are alive, 2 after retransplantation for chronic rejection subsequent to arrest of immunosuppression. The fourth died from bone marrow aplasia. Three patients with multiorgan involvement died from multisystemic failure. The remaining 3 patients had a pseudotumoral mass. Two of these are alive, 1 after retransplantation for hepatic localization and secondary vascular and biliary complication. The last died from cachexia. Four patients developed the syndrome after viral reactivation, and 6 after primo infection. Four patients were under FK506 rescue therapy. We conclude that a high rate of EBV primo infection is observed in the first months after transplantation. A significant percentage will develop EBV-associated lymphoproliferative disease, which causes death in half of the patients, including all these with multiorgan involvement. Half of the patients may survive, but because immunosuppression must be stopped, retransplantation for chronic rejection is often necessary in survivors. 相似文献
983.
RK Khanna CJ Pham GM Malik EM Spickler B Mehta ML Rosenblum 《Canadian Metallurgical Quarterly》1997,86(5):893-897
Bilateral superior ophthalmic vein (SOV) enlargement has rarely been shown to occur in patients with septic and aseptic cavernous sinus thrombosis, Graves' disease due to obstruction of the SOV by enlarged extraocular muscles, or carotid-cavernous fistulas caused by retrograde flow. The authors describe 11 patients with bilateral SOV enlargement associated with cerebral swelling as detected by computerized tomography scanning. The bilaterally enlarged SOVs returned to a normal size following resolution of cerebral swelling and elevated intracranial pressure. To the authors' knowledge, this is the first report of bilateral SOV enlargement associated with diffuse cerebral swelling that subsequently resolved after treatment of the cerebral edema. The authors believe that the bilateral SOV enlargement was caused by mechanical cavernous sinus venous stagnation due to cerebral swelling, a syndrome that occurs more commonly than currently appreciated. 相似文献
984.
R Hernández Rastrollo E Agulla Rodi?o EM Martínez Tallo J Espinosa Ruiz-Cabal J Mediero Almendros 《Canadian Metallurgical Quarterly》1996,45(6):626-630
OBJECTIVE: Percutaneous silastic central venous catheters have contributed to improve the care of neonates. They are quite safe; however, sometimes complications occur, with infections being the most frequent. A prospective study was undertaken in our NICU to know the rate of catheter-related sepsis, the influence of the duration of catheterization, the predominant portal of entry and the microorganisms isolated. PATIENTS AND METHODS: Fifty-two catheters were analyzed. Cultures were obtained once a week by aspiration from the catheter hub, the luer-lock connection and parenteral nutrition solution directly from the bag. If sepsis was suspected, blood cultures were obtained from a different vein. The tip was cultured after catheter withdrawal by the semiquantitative technique of Maki. RESULTS: Nineteen catheters (36.5%), 19 luer-lock connections (21.3%) and 7 parenteral nutrition solutions were colonized. We found a significant increase of the rate of colonization after the catheter had been in place 3 weeks or more (p < 0.05). Coagulase negative Staphylococcus was isolated in 75.7% of the samples. The rate of catheter related sepsis was 15.4% (7/8 caused by coagulase negative Staphylococcus). CONCLUSIONS: Catheter related sepsis may be more frequent than expected it colonization of the catheter were analyzed systematically. Screening catheter colonization allows an earlier diagnosis of pathogens if sepsis develops. Finally, we believe that the use of sterile techniques to handle the catheter and connections will further decrease catheter related infections. 相似文献
985.
Ad libitum ingestive behavior of rats with area postrema lesions (APX) was monitored electronically every 6 s for 23 hr. Whereas control rats ate on average 32.2 g of food each day in 16.3 distinct bouts, rats with APX ate comparable amounts of food (28.6 g) in much fewer daily bouts (5.8) that were very large. Controls drank 38.4 ml of water daily in 17.8 bouts, whereas rats with APX consumed more than twice as much water (101.5 ml) in a similar number of bouts (18.5). Controls drank 5.3 ml of 0.5 M NaCl daily in 7.0 bouts, whereas rats with APX consumed 9 times as much saline (45.5 ml) in more bouts (18.2) that were relatively large. These and other results suggest that the area postrema plays an important role in detecting inhibitory signals generated by food or fluid intake and that feeding and drinking bouts may increase in size after APX, because the feedback inhibition provided by those signals is diminished. 相似文献
986.
MC Stuart EM Bevers P Comfurius RF Zwaal CP Reutelingsperger PM Frederik 《Canadian Metallurgical Quarterly》1995,74(4):1145-1151
Phosphatidylserine (PS) is normally restricted to the inner leaflet of the plasma membrane of cells (including blood platelets). Upon cell activation PS may become exposed to the outer surface of the cell. Cell membranes with surface exposed PS at the outside form a catalytic surface for coagulation reactions. When platelets are activated with ionophore or with thrombin in combination with thapsigargin, calcium induced scrambling of phospholipids takes place, resulting in PS exposure. Concomitant with PS exposition structural changes take place. On resting and activated platelets we combined the immunocytochemical detection of surface exposed PS with (ultra)structural information. Blood platelets were activated in the presence of annexin V, a protein which binds to PS in the presence of Ca2+. Annexin V was found to bind to lipid bilayers containing more than 5 mole % PS as estimated by binding of fluorescent-labelled annexin V to liposomes with varying PS concentrations. After vitrification, freeze-substitution and embedding of the platelets, annexin V was located on ultra thin sections, as detected by an anti-annexin V antibody and gold labelled protein A. Upon activation, the platelets show two different forms; irregular platelets with unchanged cytoplasm and round cells with apparently diluted cytoplasm. Activation with ionophore initially resulted in both forms, but after ten minutes only round platelets with diluted cytoplasm were observed. Both forms of these platelets as well as the microvesicles were found to be annexin V positive. However upon activation with thrombin in combination with thapsigargin, only the round cells with diluted cytoplasm and microvesicles were annexin V positive, whereas platelets with unchanged cytoplasm, even when microvesicles are present, are negative for annexin V. 相似文献
987.
The role of the airway circulation in supporting mucociliary function has been essentially unstudied. We evaluated the airway clearance of inert, insoluble particles in anesthetized ventilated sheep (n = 8), in which bronchial perfusion was controlled, to determine whether airway mucosal blood flow is essential for maintaining surface transport of particles through airways. The bronchial branch of the bronchoesophageal artery was cannulated and perfused with autologous blood at control flow (0.6 ml.min-1.kg-1) or perfusion was stopped. With the sheep in a supine position and after a steady-state 133Xe ventilation scan for designation of lung zones of interest, an inert 99mTc-labeled sulfur colloid aerosol (2.1-microns diameter) was deposited in the lung. The clearance kinetics of the radiolabeled particles were determined from the activity-time data obtained for right and left lung zones. At 60 min postdeposition of aerosol, average airway particle retention for control bronchial blood flow conditions was 57 +/- 7 (SE)% for the right and 53 +/- 8% for the left lung zones. Clearance of particles was significantly impaired when bronchial blood flow was stopped, e.g., right and left lung zones averaged 77 +/- 6 and 76 +/- 7% at 60 min, respectively (P < 0.05). These data demonstrate a significant influence of the bronchial circulation on mucociliary transport of insoluble particles. Potential mechanisms that may account for these results include the importance of the bronchial circulation for nutrient flow, maintenance of airway wall temperature and humidity, and release of mediators and sequelae associated with tissue ischemia. 相似文献
988.
J Chan BR Smoller SP Raychauduri WY Jiang EM Farber 《Canadian Metallurgical Quarterly》1997,289(11):611-616
In order to evaluate more fully the role of neuropeptides in the pathogenesis of psoriasis, skin biopsies were obtained from 36 patients with psoriasis to identify substance P (SP), vasoactive intestinal peptide (VIP) and calcitonin gene-related peptide (CGRP). Lesional and nonlesional skin was examined from these biopsies and the results compared with those from biopsies taken from patients with a variety of other inflammatory dermatoses, including lichen planus, lichen simplex chronicus, spongiotic dermatitis, and seborrheic dermatitis. Also studied was a series of nine biopsies taken from patients with no known skin disorders. We found an increase in the number of SP-positive nerve fibers within the epidermis in biopsies from lesional skin of psoriasis patients (8.4 nerves per 3-mm biopsy) compared with nonlesional psoriatic skin (2.6 nerves per 3-mm biopsy) and normal skin (2.0 nerves per 3 mm biopsy). Other inflammatory disorders also demonstrated fewer SP-positive nerves than lesional psoriatic skin; lichen planus (0 nerves per 3 mm biopsy) and lichen simplex chronicus (1.3 nerves per 3 mm biopsy). The difference in SP-positive nerve expression between lesional psoriatic skin and the group comprising nonlesional skin, normal skin, lichen planus, and lichen simplex chronicus attained statistical significance (P < 0.013). SP-positive intraepidermal nerve fibers in lesional psoriatic specimens were fewer than in spongiotic dermatitis (17.4 nerves per 3 mm biopsy). There was no significant difference in numbers of VIP- or CGRP-immunopositive intraepidermal nerve fibers between psoriatic skin and the group comprising all other material tested. However, in five patients with psoriasis, there was a marked increase in the expression of intraepidermal CGRP (up to 10.7 nerves per 3-mm biopsy) and VIP (up to 8.3 nerves per 3-mm biopsy) which was not observed in control groups. These findings suggest that neuropeptides SP, CGRP, and VIP play a role in the pathogenesis of psoriasis. 相似文献
989.
An abdominal mass was palpated in an asymptomatic adult during a routine medical check-up. Ultrasonography and computed tomography scan diagnosed a simple renal cyst, a mesenteric cyst and a seminal vesicle cyst. At laparotomy a complete ureteral duplication and a giant ectopic megalo-ureter were diagnosed. Other complications were ruled out in the follow-up. Ureterectomy without heminephrectomy was performed and the patient remains asymptomatic 5 years after surgery. 相似文献
990.