全文获取类型
收费全文 | 8032篇 |
免费 | 797篇 |
国内免费 | 6篇 |
出版年
2022年 | 47篇 |
2021年 | 80篇 |
2020年 | 55篇 |
2019年 | 83篇 |
2018年 | 98篇 |
2017年 | 101篇 |
2016年 | 155篇 |
2015年 | 286篇 |
2014年 | 292篇 |
2013年 | 406篇 |
2012年 | 547篇 |
2011年 | 515篇 |
2010年 | 330篇 |
2009年 | 320篇 |
2008年 | 509篇 |
2007年 | 519篇 |
2006年 | 463篇 |
2005年 | 479篇 |
2004年 | 468篇 |
2003年 | 435篇 |
2002年 | 354篇 |
2001年 | 89篇 |
2000年 | 77篇 |
1999年 | 90篇 |
1998年 | 111篇 |
1997年 | 90篇 |
1996年 | 87篇 |
1995年 | 75篇 |
1994年 | 59篇 |
1993年 | 74篇 |
1992年 | 77篇 |
1991年 | 65篇 |
1990年 | 67篇 |
1989年 | 69篇 |
1988年 | 68篇 |
1987年 | 56篇 |
1986年 | 48篇 |
1985年 | 57篇 |
1984年 | 64篇 |
1983年 | 61篇 |
1982年 | 63篇 |
1981年 | 56篇 |
1980年 | 62篇 |
1979年 | 56篇 |
1978年 | 42篇 |
1977年 | 36篇 |
1976年 | 42篇 |
1975年 | 39篇 |
1974年 | 61篇 |
1973年 | 45篇 |
排序方式: 共有8835条查询结果,搜索用时 15 毫秒
81.
INTESTINAL TRIGLYCERIDE ABSORPTION IN THE RAT : An Electron Microscopical Study 总被引:22,自引:16,他引:6 下载免费PDF全文
Robert R. Cardell Jr. Susan Badenhausen Keith R. Porter 《The Journal of cell biology》1967,34(1):123-155
This report provides information on the morphology of fat absorption in rat intestinal epithelial cells. Three types of experiments were performed: (a) intubation of corn oil into fasted rats, (b) injection of physiological fatty-chyme prepared from fat-fed donor rats into ligated segments of jejunum of fasted animals, and (c) administration of electron-opaque particles in corn oil and markers given concurrently with the fat. These results support the hypothesis that fat is absorbed by selective diffusion of monoglycerides and fatty acids from micelles rather than by pinocytosis of unhydrolized triglycerides. Evidence is presented that the pits between the microvilli, previously believed to function in the transport of fat, are not involved in this process. Instead they appear to contribute their contents to lysosomes in the apical cytoplasm. Arguments are offered that the monoglycerides and fatty acids diffuse from the micelle while the latter is associated with the microvillous membrane of the absorptive cell. These micellar components penetrate the plasma membrane and diffuse into the cytoplasmic matrix where they encounter the SER. Triglyceride synthesis occurs in the SER and results in the deposition of fat droplets within its lumina. The synthesis of triglycerides and their sequestration into the SER establishes an inward diffusion gradient of monoglycerides and fatty acids. 相似文献
82.
83.
Specializations of the unit membrane 总被引:16,自引:0,他引:16
84.
85.
86.
Studies on the Endoplasmic Reticulum : IV. Its Form and Distribution during Mitosis in Cells of Onion Root Tip 总被引:28,自引:24,他引:4 下载免费PDF全文
Cells of onion and garlic root tips were examined under the electron and phase contrast microscopes after fixation in KMnO4. Special attention was focused on the distribution and behavior of the endoplasmic reticulum (ER) during the several phases of mitosis. Slender profiles, recognized as sections through thin lamellar units of the ER (most prominent in KMnO4-fixed material), are distributed more or less uniformly in the cytoplasm of interphase cells and show occasional continuity with the nuclear envelope. In late prophase the nuclear envelope breaks down and its remnants plus cytoplasmic elements of the ER, which are morphologically identical, surround the spindle in a zone from which mitochondria, etc., are excluded. During metaphase these ER elements persist and concentrate as two separate systems in the polar caps or zones of the spindle. At about this same time they begin to proliferate and to invade the ends of the spindle. The invading lamellar units form drape-like partitions between the anaphase chromosomes. In late anaphase, their advancing margins reach the middle zone of the spindle and begin to fray out. Finally, in telophase, while elements of the ER in the poles of the spindle coalesce around the chromosomes to form the new envelope, the advancing edges of those in the middle zone reticulate at the level of the equator to form a close lattice of tubular elements. Within this, which is identified as the phragmoplast, the earliest signs of the cell plate appear in the form of small vesicles. These subsequently grow and fuse to complete the separation of the two protoplasts. Other morphological units apparently participating in mitosis are described. Speculation is provided on the equal division or not of the nuclear envelope and the contribution the envelope fragments make to the ER of the new cell. 相似文献
87.
Vanillic, syringic, gallic, and protocatechuic acids, methyl-p-hydroxybenzoate, and propyl-p-hydroxybenzoate generally inhibited respiration in vitro of Escherichia coli, Proteus vulgaris, Pseudomonas aeruginosa, and Aerobacter aerogenes in human urine. In the absence of any other available carbon source, certain of the phenolic compounds were utilized. Reproduction was generally suppressed in urine buffered to pH 7, 5.6, 4.5, and 4.0. The phenolic compounds were used in the range of 0.11 to 0.99 μmole/ml. 相似文献
88.
89.
Sites of Tubulin Polymerization in PC 12 Cells 总被引:2,自引:0,他引:2
The site at which tubulin enters into polymer in the neuritic process is a very important datum in terms of our understanding of the mechanism of transport of the microtubular cytoskeleton out the axon. If the form of tubulin being transported out the axon is the microtubule, then assembly of tubulin into microtubules should occur at or near the cell body; if, however, the form of tubulin transported is free tubulin dimer, then assembly can occur at any free microtubule end out the neurite. We have injected a fluorescent analog of tubulin into differentiated PC 12 cells and used differential extraction protocols to extract free dimer but not microtubules. We have imaged these cells before and after extraction by low-light-level video fluorescence microscopy and have used image analysis to examine the sites of tubulin incorporation into polymer or other unextracted components as a function of time. We find that tubulin in the distal reaches of the neurite is found initially as monomer and that its appearance in the unextracted component occurs later. This pattern of appearance of fluorescent tubulin initially in the soluble fraction and later in the unextractable component is qualitatively similar to that reported by other workers for biotinylated tubulin, but we see a larger gap between the rates of appearance in soluble fraction and in polymer. Quantitative analysis of fluorescence intensities in the two compartments with distance out the neurite reveals substantial variation between different neurites: In some neurites, the pattern of variation of unextracted/total tubulin suggests that tubulin enters into the unextracted component primarily near the cell body and that this unextracted component moves out the neurite with time, and in other neurites it suggest that monomer adds into microtubule ends staggered out the neurite. In no case do we see a pattern suggesting that distal addition predominates. These analyses of fluorescence intensities in extracted and unextracted neurites suggest that both transport of polymerized microtubules and monomer addition onto staggered microtubule ends occur in PC12 neurites and that in individual neurites one or the other of these two behaviors may predominate. 相似文献
90.
Physical mapping of the von Recklinghausen neurofibromatosis region on chromosome 17 总被引:15,自引:9,他引:6 下载免费PDF全文
Jane W. Fountain Margaret R. Wallace Anne M. Brereton Peter O''''Connell Raymond L. White Donna C. Rich David H. Ledbetter Robin J. Leach R. E. Keith Fournier Anil G. Menon James F. Gusella David Barker Karen Stephens Francis S. Collins 《American journal of human genetics》1989,44(1):58-67
The von Recklinghausen neurofibromatosis (NF1) locus has been linked to chromosome 17, and recent linkage analyses place the gene on the proximal long arm. NF1 probably resides in 17q11.2, since two unrelated NF1 patients have been identified who possess constitutional reciprocal translocations involving 17q11.2 with chromosomes 1 and 22. We have used a somatic-cell hybrid from the t(17;22) individual, along with other hybrid cell lines, to order probes around the NF1 locus. An additional probe, 17L1, has been isolated from a NotI linking library made from flow-sorted chromosome 17 material and has been mapped to a region immediately proximal to the translocation breakpoint. While neither NF1 translocation breakpoint has yet been identified by pulse-field gel analysis, an overlap between two probes, EW206 and EW207, has been detected. Furthermore, we have identified the breakpoint in a non-NF1 translocation, SP-3, on the proximal side of the NF1 locus. This breakpoint has been helpful in creating a 1,000-kb pulsed-field map, which includes the closely linked NF1 probes HHH202 and TH17.19. The combined somatic-cell hybrid and pulsed-field gel analysis we report here favors the probe order D17Z1-HHH202-TH17.19-CRYB1-17L1-NF1- (EW206, EW207, EW203, L581, L946)-(ERBB2, ERBA1). The agreement in probe ordering between linkage analysis and physical mapping is excellent, and the availability of translocation breakpoints in NF1 should now greatly assist the cloning of this locus. 相似文献