全文获取类型
收费全文 | 97100篇 |
免费 | 7694篇 |
国内免费 | 33篇 |
专业分类
104827篇 |
出版年
2021年 | 833篇 |
2018年 | 1300篇 |
2017年 | 1212篇 |
2016年 | 1634篇 |
2015年 | 1726篇 |
2014年 | 2082篇 |
2013年 | 2960篇 |
2012年 | 3238篇 |
2011年 | 3340篇 |
2010年 | 2488篇 |
2009年 | 2098篇 |
2008年 | 3044篇 |
2007年 | 2998篇 |
2006年 | 2823篇 |
2005年 | 2659篇 |
2004年 | 2653篇 |
2003年 | 2542篇 |
2002年 | 2363篇 |
2001年 | 4397篇 |
2000年 | 4152篇 |
1999年 | 3223篇 |
1998年 | 1042篇 |
1997年 | 1034篇 |
1996年 | 916篇 |
1995年 | 834篇 |
1993年 | 830篇 |
1992年 | 2443篇 |
1991年 | 2453篇 |
1990年 | 2456篇 |
1989年 | 2202篇 |
1988年 | 2065篇 |
1987年 | 1977篇 |
1986年 | 1826篇 |
1985年 | 1818篇 |
1984年 | 1495篇 |
1983年 | 1296篇 |
1982年 | 929篇 |
1981年 | 873篇 |
1979年 | 1436篇 |
1978年 | 1126篇 |
1977年 | 1015篇 |
1976年 | 973篇 |
1975年 | 1156篇 |
1974年 | 1255篇 |
1973年 | 1337篇 |
1972年 | 1184篇 |
1971年 | 1043篇 |
1970年 | 924篇 |
1969年 | 955篇 |
1968年 | 836篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
Summary Glomus (Type I) cells of the carotid body of adult rats were studied electron microscopically after fixation with potassium permanganate or with glutaraldehyde and osmium tetroxide. Two permanganate fixation methods (using Krebs-Ringer-glucose, pH 7.0, or acetate buffer, pH 5.0) were compared. Numerous dense-cored vesicles were observed only in about one tenth of the glomus cells when neutral permanganate was used for fixation, although all glomus cells showed such vesicles after fixation with glutaraldehyde and osmium tetroxide. Numerous vesicles with a dense core were observed in about one third of the cells after fixation with acid potassium permanganate. With this fixation, small dense-cored vesicles similar to those in adrenergic nerve terminals were occasionally seen in the cytoplasm of glomus cells. It is tentatively concluded that the amine-storing vesicles of the carotid body are different from those in the small intensely fluorescent (SIF) cells and those in adrenergic nerve terminals. 相似文献
992.
Summary Unique fusiform or spindle-shaped particles (Phi bodies) and rods with hydroperoxidase (catalase and/or peroxidase) activity are present in human granulocyte precursors only in acute myelogenous leukemia (AML). These newly recognized particles are much more numerous and prominent than Auer rods. They may be rapidly and readily identified using the microscope in marrow or peripheral blood films when the procedures recommended in this paper for fixation, incubation for hydroperoxidase demonstration in 3,3-diaminobenzidine (DAB)/H2O2 medium, copper salt treatment and counterstaining (optional) with the Papanicolaou method are employed. Films prepared in the same manner but treated with benzidine/H2O2 medium for myeloperoxidase did not reveal these particles.We believe that Phi bodies are pathognomonic of AML since they are almost invariably present in AML patients with active disease. Their presence serves to distinguish AML from acute lymphocytic leukemia and from chronic granulocytic leukemia in blast crisis. Since the particles disappear in disease remission and reappear upon relapse, the recommended procedure is not only useful in diagnosis but in guiding therapy.When a very rapid diagnosis is needed, it is not necessary to counterstain the preparations, but the nuclei, cytoplasm and plasmalemma can readily be observed in the granulocyte precursors when they are counterstained by the Papanicolaou method. This treatment does not diminish the clarity of the Phi bodies and rods which stain by virtue of their peroxidatic activity.This cytochemical diagnostic procedure should be considered for adoption by hematology laboratories.This investigation was supported by NIH research grants DE02668, CA11265, DE04730, and RR05333 相似文献
993.
994.
Light and Electron Microscopic Observations of Gametogenesis in Hastigerina pelagica (Foraminifera)*
M. SPINDLER O. R. ANDERSON C. HEMLEBEN A. W. H. B 《The Journal of eukaryotic microbiology》1978,25(4):427-433
SYNOPSIS. During gametogenesis mother individuals of Hastigerina pelagica (d'Orbigny) undergo significant morphological changes. Thirty h before gamete release, the cytoplasm changes from pale orange to bright red, possibly due to transport of stored lipids from the inner region to more peripheral parts of the cytoplasm. During the next 10 to 15 h the bubble capsule which surounds the calcareous shell is discarded. After all bubbles have disappeared, the individual sheds its spines by resorbing the spine bases close to the shell surface. A single mother nucleus divides into some hundreds of thousands of gamete nuclei within a span of ~ 20 h. A bulge of cytoplasm is extruded from the aperture and increases in size during the next 5 to 10 h. This bulge consists of cytoplasmic strands in which gametes and spherical bodies are embedded. The gametes and spherical bodies mature and are released during the afternoon and early evening. The gametes have 2 unequal acronematic flagella. A previously undescribed structure in foraminiferal reproduction is the spherical body which consists of a large vacuole surrounded by a thin cytoplasmic layer in which several nuclei, various typical cell organelles and multiple flagella are present. The spherical bodies are believed to play a role as receptacles of waste material, possibly including residual digestive enzymes, thereby protecting the gametes from lysis during the reproductive process. Fusion of gametes and further development into the next generation have not been observed. 相似文献
995.
996.
A photomap of the banding pattern of the salivary gland chromosomes of Anopheles stephensi Liston, which is first of its kind, has been prepared. The salivary chromosome complement consists of five arms, the shortest of which represents the telocentric X-chromosome, and the remaining four the autosomal arms. A comparison has been made of the banding pattern of this species with other species of the subgenus Cellia. 相似文献
997.
R Wever J H Van Drooge A O Muijsers E P Bakker B F Van Gelker 《European journal of biochemistry》1977,73(1):149-154
The effect of CO on the optical absorbance spectrum of partially reduced cytochrome c oxidase has been studied. The changes at 432 and 590 nm suggest that the cytochrome alpha2/3+ - CO compound is formed preferentially and that concomitantly a second electron is taken up by the enzyme. From the CO-induced changes at 830 nm it is concluded that in the partially reduced enzyme addition of CO causes reoxidation of the copper component of cytochrome c oxidase. Addition of CO to partially reduced enzyme (2 electrons per 4 metal ions) also brings about a decrease in the intensities of electron paramagnetic resonance signals of high-spin heme iron near g = 6 and of the low-spin heme at g = 2.6. Concomitantly both the low-spin heme a signal at g = 3 and the copper signal at g = 2 increase in intensity. These results demonstrate that formation of the reduced diamagnetic cytochrome a3 - CO compound is accompanied by reoxidation of both the copper component detectable by electron paramagnetic resonance and possibly also by cytochrome a. 相似文献
998.
999.
Nganasans is a small samodyen-speaking ethnic group originated from several clans of reindeer hunters. Pedigree studies revealed no consanguineous matings of uncle-niece, aunt-nephew, first cousins type among 120 families studied. Rather rarely mating between second cousins could be observed. The reviewed traditional kindship system based on bilateral exogamy is an explanation. Data on 12 blood systems and 6 red cell enzymes distribution in two main localities almost totally studied have been presented. No A2, r, K, MS alleles were observed. Hgh frequencies of Ns, R2, Fya, Jka, Gm1 have been found. Diegoa was seen in only one family. Polymorphism on PGM1, 6-PGD, AK and AP, monomorphism on LDH and MDH has been observed. 相似文献
1000.
The paper explains how the formulas for calculating the surface area of the prolate spheroid, which a nucleus resembles, can be changed by suitable substitutions into formulas based on measured diameters l and k [mm] of the nucleus approach side surface, magnified 3.000 times, and on a mixed cyclometric function dependent on the axial ratio. Their values established for distinct axial ratios are compiled in a table. The values of the mixed cyclometric function are to be calculated for any other axial ratio according to a formula based on linear interpolation. The nucleus surface Omu is obtained in the natural order of magnitude [micron2]. In case of constant axial ratio, the surface area values form a second-order arithmetic progression, and a recursion formula has been developed to check the values of its terms. In case of nuclei of spherical shape or constant small diameter k, the surface area formulas may be simplified. Numeral examples serve for explanation. For all measured-value combinations involved, a second part, which is being prepared, will contain a complete table of function values, which is referred to in the Appendix and from which the values of the natural surface areas of spheroid nuclei can be gathered. 相似文献