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21.
Masahiko Kuroda Hajime Horiuchi Teruaki Oka Tsuyoshi Ishida Akira Ono Masao Kawakita Rikuo Machinami 《Virchows Archiv : an international journal of pathology》1993,423(3):209-213
Ninety-one cases of human bone and soft tissue tumours were studied for calcium pump expression by strepto-avidin-biotin immunohistochemical staining with a monoclonal antibody against sarcoplasmic reticulum calcium-ATPase (mAb6F5). Two out of 5 cases of embryonal rhabdomyosarcoma, 1 out of 5 cases of biphasic synovial sarcoma, 4 of 4 cases of chordoma and all of 3 chondrosarcoma cases were positive for mAb6F5. Although this novel monoclonal antibody can be used as a marker of myogenic tumours, the present positive result for endoplasmic reticulum calcium-ATPase (calcium pump) in other tumours including chordoma, chondrosarcoma and synovial sarcoma indicates a wider immunoreactivity. The findings further suggest that intracellular calcium may play an important role in cell proliferation and/or differentiation. 相似文献
22.
The increased rate of Ca2+ uptake and ATPase activity in isolated cardiac sarcoplasmic reticulum (SR) by adenosine 3,5-monophosphate (cAMP) has been shown to be activated by a cAMP-dependent protein kinase (cAMP kinase). Functionally skinned myocardial fiber preparations were used to study the mechanisms of cAMP action on the SR at the same time that tension was monitored. cAMP effects were studied on Ca2+-activated tension of the contractile proteins, and on Ca2+ uptake and release from the SR using caffeine-induced tension transients. Neither cyclic AMP (0.1–5 M) nor the catalytic subunit of cAMP kinase (0.1–1 M) (PK-C) significantly changed either the maximal or the submaximal Ca2+-activated tension. The areas of the tension transients were unchanged when cAMP was present in the releasing solution (release phase), and were significantly increased up to a mean of about 80% when cAMP or PK-C was present in the Ca2+ loading solutions (uptake phase). The increased tension transient was blocked by the heat-stable inhibitor of cAMP kinase. We conclude that cAMP-induced increases in Ca2+ uptake by the SR could play an important role in the positive inotropic effect. cAMP kinase could thus play a crucial role in the regulation of myocardial contractility. 相似文献
23.
Mechanically skinned skeletal muscle fibres from rat and toad were exposed to the permeabilizing agents β-escin and saponin.
The effects of these agents on the sealed transverse tubular system (t-system) and sarcoplasmic reticulum (SR) were examined
by looking at changes in the magnitude of the force responses to t-system depolarization, the time course of the fluorescence
of fura-2 trapped in the sealed t-system, and changes in the magnitude of caffeine-induced contractures following SR loading
with Ca2+ under defined conditions. In the presence of 2 μg ml–1β-escin and saponin, the response to t-system depolarization was not completely abolished, decreasing to a plateau, and a
large proportion of fura-2 remained in the sealed t-system. At 10 μg ml–1, both agents abolished the ability of both rat and toad preparations to respond to t-system depolarization after 3 min of
exposure, but a significant amount of fura-2 remained in sealed t-tubules even after exposure to 100 μg ml–1β-escin and saponin for 10 min. β-Escin took longer than saponin to reduce the t-system depolarizations and fura-2 content
of the sealed t-system to a similar level. The ability of the SR to load Ca2+ was reduced to a lower level after treatment with β-escin than saponin. This direct effect on the SR occurred at much lower
concentrations for rat (2 μg ml–1β-escin and 10 μg ml–1 saponin) than toad (10 μg ml–1β-escin and 150 μg ml–1 saponin). The reverse order in sensitivities to β-escin and saponin of t-system and SR membranes indicates that the mechanisms
of action of β-escin and saponin are different in the two types of membrane. In conclusion, this study shows that: (1) β-escin
has a milder action on the surface membrane than saponin; (2) β-escin is a more potent modifier of SR function; (3) simple
permeabilization of membranes is not sufficient to explain the effects of β-escin and saponin on muscle membranes; and (4)
the t-system network within muscle fibres is not a homogeneous compartment.
Received: 18 November 1998 / Received after revision: 6 January 1999 / Accepted: 7 January 1999 相似文献
24.
25.
衰老是在细胞、组织和器官水平上发生的生理性内稳态的渐进性损害过程。就代谢角度而言,该过程主要表现为体成分、胰岛素抵抗、自噬功能障碍、线粒体和炎症反应的变化,其中涉及生长激素、胰岛素/胰岛素样生长因子1及各种能量感应系统如AMP活化蛋白激酶(AMP-activated protein kinase,AMPK). 相似文献
26.
C. H. Orchard G. L. Smith D. S. Steele 《Pflügers Archiv : European journal of physiology》1998,435(4):555-563
Rat ventricular trabeculae were mounted for isometric tension recording, and then permeabilized with saponin. The Ca2+ concentration ([Ca2+]) within the permeabilized preparation (cytosolic [Ca2+]) was monitored continuously using Indo-1 and the integrals of Ca2+ transients resulting from brief caffeine application used as an index of the sarcoplasmic reticulum (SR) Ca2+ content. The relationship between SR Ca2+ content and cytosolic [Ca2+] was studied within the reported physiological range (i.e. 50–250 nmol · l–1 Ca2+). Increasing cytosolic [Ca2+] from 50 nmol · l–1 to 250 nmol · l–1 increased the steady-state SR Ca2+ content about threefold. However, increasing [Ca2+] above 250 nmol · l–1 typically resulted in spontaneous SR Ca2+ release, with no further increase in SR Ca2+ content. The SR Ca2+ content increased only slowly when cytosolic [Ca2+] was increased; it was unchanged 20 s after a rapid increase in cytosolic [Ca2+], but increased progressively to a new steady-state level during the following 1–2 min. In a parallel series of experiments
using intact papillary muscles, increasing extracellular [Ca2+] (from 0.5 to 5 mmol · l–1) significantly increased twitch tension within 20 s of the solution change. These results support previous suggestions that
the SR Ca2+ content may increase when diastolic cytosolic [Ca2+] rises during inotropic interventions such as increased stimulus rate or extracellular [Ca2+]. However, the rate at which SR Ca2+ responds to changes in cytoplasmic [Ca2+] within the diastolic range does not appear rapid enough to explain the early potentiation of twitch tension in intact preparations
after an increase in extracellular [Ca2+].
Received: 26 August 1997 / Accepted: 28 October 1997 相似文献
27.
Secretion of Igs and surface expression of HLA antigens was examined in lymphoid cells as a function of temp. Upon reducing the temp from 37 to 20 degrees C a progressive decrease in the secretion of Ig and surface expression of HLA antigens was noted. When the status of the oligosaccharides present on these glycoproteins was examined, conversion of high-mannose [endo-beta-N-acetylglucosaminidase-(Endo H) sensitive] to complex-type (Endo H resistant) oligosaccharides diminished with decreasing temp. At no time was an accumulation of Endo H resistant glycoproteins seen intracellularly. These results show that the phenomenon observed for synthesis and intracellular transport of viral glycoproteins in epithelial cells at reduced temp, namely intracellular accumulation of viral glycoproteins carrying complex sugar moieties, does not necessarily apply to glycoprotein transport in lymphoid cells. A difference in subcellular organization of epithelial and lymphoid cells may be responsible for this discrepancy. 相似文献
28.
In vitro biosynthesis and core glycosylation of the histidine-rich protein of Plasmodium lophurae 总被引:2,自引:0,他引:2
We have characterized the early biosynthetic forms of the histidine-rich protein (HisRP), a major, granule-bound protein (Mr 58 000) of the avian malarial parasite Plasmodium lophurae. We have translated poly(A)-containing, size-selected parasite mRNA in the wheat germ cell-free system in the presence of [3H]histidine. HisRP was synthesized as a larger precursor (Mr 63 000). When dog pancreas microsomal membranes were present in the cell-free system during translation, a still larger form of HisRP (Mr 66 000) was detected. This larger form was segregated into the dog pancreas microsomal vesicles and was core glycosylated. Presumably, it corresponds to an intermediate form located in the parasite rough endoplasmic reticulum (RER). The difference in the Mr of approx. 8 000 between this RER associated 'pro' form and the granule-bound, mature form of HisRP suggests that proteolytic processing occurs upon transport from the RER to the granule. Segregation and core glycosylation were strictly coupled to translation and were not observed upon posttranslational addition of microsomal membranes. Thus, the early events in the biosynthesis of HisRP are similar to those established for secretory and lysosomal proteins. 相似文献
29.
Intracellular pH changes affect excitation-contraction coupling in skeletal, and cardiac muscles. However the proton implication
in modulating the sarcoplasmic reticulum Ca2+ release channel activity has never been visualized at single channel level. A large conducting Ca2+ release pathway has previously been characterized after incorporation of skeletal and cardiac sarcoplasmic reticulum vesicles
into planar lipid bilayers. This channel has been activated by micromolar and millimolar concentrations of Ca2+ and ATP, respectively. The pH was independently varied on each side of the channels. Acidification of the cis-chamber (7.4
to 6.6) induced a modification of the gating behaviour, resulting in a decrease of the open probability. This effect was completely
reversible. On the other hand, acidification of the trans-chamber (7.4 to 6.8) induced a reduction of the unitary conductance
of the sarcoplasmic reticulum Ca2+ release channel. 相似文献
30.
Objective We previously demonstrated that, when expressed in COS-7 cells, L-histidine decarboxylase (HDC), which has neither an amino
terminal signal sequence nor a hydrophobic membrane anchor, was localized in the endoplasmic reticulum (ER), although its
orientation in the membrane remains to be clarified.
Methods & Results Protease digestion and immunofluorescence analyses of the cells, of which plasma membrane was selectively permeabilized, revealed
that the amino terminal 50-kDa portion of HDC is hardly accessible to proteases and antibodies added exogenously from the
cytosolic side. Green fluorescent protein fused with the carboxyl terminal 20-kDa region of HDC at its carboxyl terminus exhibited
the same characteristics as native HDC.
Conclusion These results indicate that HDC is tightly associated with the ER membrane with its carboxyl terminal region exposed on the
cytosolic side.
Received 22 November 2005; returned for revision 28 December 2005; accepted by A. Falus 22 January 2006 相似文献